Sleep Tracking Metrics Decoded: What Each Number Means
Sleep tracking metrics include numerous measurements that can feel overwhelming. This decoder guide explains what each number means including total sleep time, efficiency, stages, heart rate variability, respiratory rate, and movement, helping you understand which metrics matter most for your specific goals.
Sleep Tracking Metrics Decoded: What Each Number Means
Waking up tired after a full night in bed is a uniquely frustrating feeling. You did the work—you got under the covers, closed your eyes, and spent hours “asleep.” Yet, the morning grogginess and mid-afternoon slump tell a different story. For decades, sleep was a black box; a mysterious, unmeasured void between bedtime and alarm. You had only a vague sense of its quality based on how you felt.
Today, technology has illuminated this darkness. With a simple wearable device, you can now generate a detailed report on your night—a dashboard filled with scores, percentages, and graphs. But this new frontier of knowledge brings a fresh challenge: a flood of data without a clear manual. What does a “Sleep Score” of 82 really mean? Is 45 minutes of deep sleep good or bad? Why does your heart rate dip at 3 a.m.?
This article is your decoder ring. We will move beyond the simple count of hours and dive deep into the physiology behind every metric your smart ring or tracker provides. You will learn not just what the numbers are, but what they reveal about your body’s nightly repair work, your brain’s processing, and your readiness for the day ahead. This is more than data interpretation; it’s a journey toward becoming an expert on your own rest, empowered to make precise adjustments for profoundly better sleep and better days.
The New Language of Sleep: From Hours to Data
For most of human history, the primary metric for sleep was duration. The goal was simple: get enough hours. While quantity is undeniably crucial—with experts consistently recommending seven to nine hours per night for healthy adults—this single dimension tells an incomplete story. You can spend nine hours in bed but experience fragmented, shallow sleep that leaves you exhausted. Conversely, a tightly consolidated six hours of high-quality, deep, and REM-rich sleep can be profoundly restorative.
The advent of consumer sleep tracking technology has fundamentally changed this conversation. By using sensors like accelerometers to detect movement and optical heart rate monitors to track cardiac activity, these devices construct a sophisticated picture of your night. They estimate your time in different sleep stages (light, deep, and REM), measure disturbances, and calculate overall efficiency and quality scores. This data transforms sleep from a monolithic block of time into a dynamic, multi-phase process you can analyze and optimize.
This shift mirrors a broader trend in health and wellness: the move from passive observation to active, data-driven management. Just as athletes use heart rate zones to guide training, we can now use sleep architecture to guide recovery. The numbers on your morning report are not arbitrary; they are reflections of your autonomic nervous system, your cognitive processing, and your physical repair mechanisms. Learning their language is the first step toward true sleep mastery.
Total Sleep Time: The Foundational Metric
Total Sleep Time (TST) is the most straightforward metric on your report: the total number of minutes you were actually asleep during the night. It’s the foundational canvas upon which all other, more nuanced data is painted. Without adequate total time, the quality and structure of your sleep can only do so much to support recovery.
Why This Number is Non-Negotiable
Sleep science has consistently linked insufficient sleep duration—generally defined as less than seven hours per night—to a cascade of negative health outcomes. These are not minor inconveniences but serious long-term risks:
Metabolic Disruption: Regularly short sleep is associated with weight gain, obesity, and an increased risk of type 2 diabetes. It disrupts hormones that regulate hunger (ghrelin and leptin), often leading to increased appetite and cravings for high-calorie foods.
Cardiovascular Strain: Chronic sleep deprivation is a known risk factor for high blood pressure, heart disease, and stroke. During deep sleep, your heart rate and blood pressure drop, giving your cardiovascular system a vital period of rest it cannot get while awake.
Cognitive & Safety Impacts: Sleep duration directly affects mental performance. A lack of sleep impairs attention, working memory, and decision-making. It’s also associated with an increase in errors, accidents at home and work, and training injuries.
The National Sleep Foundation’s recommendation of 7-9 hours is a population-wide guideline. Your personal “sweet spot” within that range is influenced by genetics, age, and current life demands. The key is consistency and ensuring you regularly meet your individual need.
Interpreting Your Total Sleep Time
When reviewing your Total Sleep Time, context is everything:
The Goldilocks Zone: Aim to consistently fall within the 7-9 hour window. Use your daytime energy, mood, and cognitive sharpness as a biofeedback tool to fine-tune your personal ideal.
Trends Over Isolated Nights: A single short night is usually recoverable. The real concern is a trend of insufficient sleep. Your smart ring is excellent at showing your weekly and monthly averages—pay more attention to these than to any single night’s data.
The Compensation Myth: You cannot reliably "catch up" on sleep over the weekend. While extra rest can help alleviate acute sleep debt, it does not fully reverse the metabolic and cognitive toll of consistent weekday shortfalls. The goal is sustainable, nightly adequacy.
Think of Total Sleep Time as the non-negotiable deposit you must make into your health bank each night. All other metrics represent the interest you earn on that deposit. The larger and more consistent the deposit, the greater the potential return in terms of recovery, performance, and well-being.
Sleep Efficiency: The Measure of Sleep Consolidation
If Total Sleep Time tells you how much you slept, Sleep Efficiency tells you how well you used your time in bed. It is a critical ratio that exposes the hidden cost of restlessness and wakefulness.
Sleep Efficiency is calculated as a simple percentage: (Total Sleep Time / Total Time in Bed) x 100. For example, if you spent 8 hours (480 minutes) in bed but were only asleep for 7 hours (420 minutes), your sleep efficiency is (420 / 480) x 100 = 87.5%.
What Does Your Percentage Mean?
This single number is a powerful indicator of sleep consolidation:
85% and Above (Excellent): This is the target zone. It indicates that once you got into bed, you fell asleep relatively quickly, experienced minimal prolonged awakenings, and slept soundly through most of the night. Your time in bed was used efficiently for its intended purpose.
80-84% (Good): This is a solid, healthy range for most adults. It suggests minor periods of wakefulness or a slightly longer time to fall asleep, but overall good sleep consolidation.
Below 80% (Needs Attention): An efficiency score consistently below 80% signals fragmented sleep. This could manifest as trouble falling asleep (long sleep latency), frequent middle-of-the-night awakenings, or waking up very early and being unable to drift off again. This fragmentation prevents you from progressing smoothly through complete sleep cycles, robbing you of deep and REM sleep even if your total time in bed seems sufficient.
The Hidden Disruptors of Sleep Efficiency
A low Sleep Efficiency score is a flag to investigate the "why." Common culprits include:
Sleep Environment: An uncomfortable mattress, a room that’s too warm or too cold, or exposure to light and noise.
Lifestyle Factors: Consumption of caffeine or alcohol too close to bedtime, late-night heavy meals, or using electronic devices in bed.
Stress and Anxiety: A racing mind is one of the most common barriers to falling and staying asleep.
Improving your Sleep Efficiency is often the most impactful way to enhance sleep quality without going to bed earlier. It’s about creating conditions that allow for seamless, uninterrupted rest. For more actionable strategies on building these conditions, you can explore our dedicated wellness blog.
The Sleep Stages: Light, Deep, and REM – Your Nightly Repair Cycle
Sleep is not a uniform state. Throughout the night, your brain and body cycle through distinct stages, each with a unique physiological purpose. Consumer trackers categorize these into three main types: Light Sleep, Deep Sleep, and REM (Rapid Eye Movement) Sleep. Understanding the role of each stage transforms your data from a simple pie chart into a story of nightly renewal.
Light Sleep: The Gateway and Regulator
Light Sleep is the most abundant stage, typically comprising about 50% of an adult’s total sleep. It acts as the transition zone between wakefulness and deeper sleep.
What Happens Here: Your body begins to disengage from the environment. Your heart rate and breathing slow, body temperature drops, and muscles relax. This stage is crucial for memory processing and metabolism regulation. It’s also the easiest stage from which to be awakened.
Interpreting Your Data: A healthy percentage of light sleep is essential. Don’t be alarmed by its dominance on your chart. However, an unusually high percentage of light sleep, especially when coupled with low deep or REM sleep, can indicate fragmented sleep where you’re not progressing fully into more restorative stages.
Deep Sleep: The Physical Restoration Phase
Deep Sleep, or slow-wave sleep, is the most physically restorative phase. It is the "deepest" point in the sleep cycle, when you are hardest to awaken.
What Happens Here: This is your body’s prime time for repair. Human growth hormone is released, driving tissue growth, muscle repair, and cellular regeneration. Your immune system is strengthened, and energy stores are replenished. Deep sleep is also when the brain clears out metabolic waste products.
Interpreting Your Data: Deep sleep is prioritized in the first half of the night. A typical adult might spend 10-25% of their night (roughly 48-120 minutes in an 8-hour sleep) in deep sleep. Consistently low deep sleep can be a sign of chronic sleep deprivation, high stress, or frequent disruptions. It’s why you feel physically drained after a night of poor sleep.
REM Sleep: The Mental and Emotional Processing Phase
REM Sleep is characterized by rapid eye movements, vivid dreams, and a brain activity pattern similar to being awake.
What Happens Here: This stage is essential for cognitive functions, memory consolidation, learning, and emotional regulation. Your brain processes the day’s experiences, solidifies memories, and makes creative connections. Your body experiences temporary muscle paralysis (atonia) to prevent you from acting out your dreams.
Interpreting Your Data: REM sleep periods become longer and more prominent in the second half of the night. It typically makes up 20-25% of total sleep (about 96-120 minutes). Suppressing REM sleep (often through alcohol or certain medications) can lead to brain fog, poor memory, and emotional irritability.
The Cyclical Dance
These stages unfold in cyclical patterns, each lasting about 90-120 minutes. A healthy night’s sleep consists of 4-6 complete cycles. In the early cycles, deep sleep dominates. As the night progresses, deep sleep wanes, and REM sleep periods extend. This architecture is why cutting your sleep short by even an hour can disproportionately rob you of crucial REM sleep, leaving you feeling mentally unfocused.
Awake Time & Wake-Ups: Quantifying Sleep Fragmentation
Even the best sleepers don’t experience a perfectly uninterrupted night. Brief awakenings are a normal part of the sleep architecture. The metrics Awake Time and Wake-Ups on your sleep report quantify this fragmentation, helping you distinguish between normal micro-arousals and disruptive sleep interruptions.
Understanding Normal vs. Disruptive Awakenings
Micro-Arousals: These are very brief (often just a few seconds) shifts to a lighter stage of sleep or wakefulness that you almost never remember. They are a natural part of transitioning between sleep cycles. A sleep report might log 3 to 5 such events per night as quite normal.
Disruptive Awake Periods: These are longer awakenings where you become consciously aware of being awake, perhaps to check the clock, adjust your bedding, or use the bathroom. These episodes fragment your sleep, potentially breaking a sleep cycle before it’s complete and making it harder to descend back into deep or REM sleep.
What Your Data Tells You
Cumulative Awake Time: This is the total sum of all minutes spent awake after initially falling asleep. While some time is expected, a cumulative awake time exceeding 30-40 minutes per night (on a consistent basis) starts to significantly erode sleep efficiency and quality.
Number of Wake-Ups: This is the count of distinct awakening events. Context matters greatly here. Five wake-ups that each last 30 seconds are far less problematic than two wake-ups that each last 20 minutes. The latter pattern is characteristic of maintenance insomnia.
Common Causes and Connections
Frequent or prolonged awakenings are rarely random. They are often signals:
Environmental Triggers: A partner’s snoring, street noise, a room that’s too hot or cold, or an uncomfortable mattress.
Physiological Factors: The need to use the bathroom (often linked to fluid intake before bed), pain or discomfort, restless leg syndrome, or undiagnosed sleep apnea, where breathing pauses cause the brain to trigger a brief awakening to restart breathing.
Lifestyle & Behavioral Factors: Alcohol consumption, while initially sedating, often leads to rebound awakenings in the second half of the night as its effects wear off. Similarly, high stress or anxiety can cause your mind to activate during the night.
Tracking these metrics over time is invaluable. You might notice, for example, that your Wake-Ups spike on nights after you have a late evening drink or when your stress levels are high according to your ring’s daily metrics. This turns vague feelings of “restless sleep” into clear, actionable data. For persistent issues, this data can be a crucial starting point for a conversation with a healthcare provider. You can learn more about how to prepare for such a discussion on our FAQ page.
Sleep Latency: The Measure of Sleep Onset
Sleep Latency—often labeled as “Time to Sleep” in apps—refers to the number of minutes it takes you to fall asleep after getting into bed and intending to sleep. This metric is a direct window into your nervous system’s ability to wind down and transition from wakefulness to rest.
The Goldilocks Zone of Falling Asleep
Ideal Range (10-20 minutes): Falling asleep within this window is generally considered healthy. It suggests you are sufficiently tired, your sleep drive is high, and your environment and mind are conducive to sleep.
Too Short (<5 minutes): While it might seem like a superpower, falling asleep almost instantly can actually be a sign of severe sleep deprivation or a sleep disorder like narcolepsy. Your body is crashing from exhaustion rather than smoothly transitioning.
Too Long (>30 minutes): Consistently taking a long time to fall asleep, known as sleep onset insomnia, is the most common complaint. It indicates that arousal (physical or cognitive) is overriding your sleep drive.
What Prolonged Latency Reveals
If your sleep latency is consistently high, it’s a signal to audit your pre-sleep routine and environment:
Cognitive Hyperarousal: This is the “racing mind.” You’re in bed, but your brain is still processing the day’s events, worrying about tomorrow, or problem-solving. This state keeps the sympathetic (“fight-or-flight”) nervous system engaged.
Behavioral Misalignment: Using your bed for work, watching stressful TV, or scrolling through social media creates a mental association between your bed and alertness, not rest.
Physiological Factors: Consuming stimulants like caffeine too late in the day, exercising vigorously right before bed, or being in a room that’s too bright or warm can all delay sleep onset.
Improving Your Sleep Latency
The goal is to build a “buffer zone” between your active day and your sleep time. This is often called sleep hygiene. Effective strategies include:
A Consistent Wind-Down Routine: Spend the last 30-60 minutes before bed doing calming activities like reading a physical book, taking a warm bath, light stretching, or practicing meditation.
Strict Bed-Boundary Rule: Reserve your bed for sleep and intimacy only. Train your brain to associate being in bed with sleeping.
Manage Light Exposure: Dim lights in the evening and minimize exposure to the blue light from screens. Consider using blue-light filtering settings on devices if you must use them.
By tracking your sleep latency, you can experiment with these strategies and see their direct impact on your data. A reduction in time to sleep is a quick, tangible win that improves sleep efficiency and sets the stage for a better night overall.
Heart Rate During Sleep: Your Nocturnal Vital Sign
Your heart doesn’t sleep when you do, but its behavior changes dramatically. Tracking your Average Nightly Heart Rate and, more importantly, its dipping pattern, provides profound insights into your recovery status, fitness, and overall health.
The Normal Nightly Dip
In a state of good health and recovery, your resting heart rate (RHR) during sleep should be significantly lower than your daytime resting rate—typically by 10-30 beats per minute (BPM). This dip is driven by the dominance of the parasympathetic nervous system (the “rest-and-digest” system), which slows the heart, lowers blood pressure, and directs energy toward restoration.
A healthy sleeping heart rate for adults generally falls between 40-85 BPM, with fit individuals and athletes often dipping into the 40s and 50s.
The lowest point usually occurs during deep sleep, when physical restoration is at its peak.
When the Dip Flattens: A Key Warning Sign
A diminished or absent nighttime heart rate dip is one of the most telling signs from your sleep data. It indicates your body is under some form of stress and cannot fully engage its recovery mode. Causes include:
Physical Stress: Overtraining, illness (even a coming cold), injury, or chronic pain.
Mental & Emotional Stress: High anxiety, depression, or chronic work stress keeps the sympathetic nervous system subtly activated.
Lifestyle Factors: Alcohol consumption before bed, large late-night meals, or sleeping in a hot environment.
Potential Health Issues: Conditions like sleep apnea, where breathing disruptions cause micro-stress events throughout the night, can prevent heart rate from dipping properly.
Tracking Trends, Not Single Nights
It’s essential to watch the trend of your sleeping heart rate, not over-interpret a single night. A temporary elevation is normal after a hard workout, a stressful day, or if you’re fighting off an illness (which your smart ring’s temperature sensor may also detect).
However, a consistent trend of a higher-than-normal sleeping heart rate or a flattened dip over several nights is your body’s clear signal that it needs more support. It may be time to prioritize rest, manage stress, hydrate, or evaluate other lifestyle factors. This kind of proactive insight is at the core of what makes 24/ wearable technology so valuable for long-term wellness. To see how others have used these insights to change their health trajectory, you can read their stories in our testimonials.
Heart Rate Variability (HRV): The Ultimate Recovery Metric
If you had to choose one number to represent your body’s readiness and resilience, Heart Rate Variability (HRV) would be a prime candidate. While it sounds complex, its interpretation is incredibly powerful for anyone focused on recovery.
What HRV Actually Measures
Contrary to what the name implies, HRV is not about how much your heart rate changes from minute to minute. Instead, it measures the tiny, millisecond variations in the time interval between each heartbeat. These variations are controlled by your autonomic nervous system (ANS).
High HRV: Indicates a strong, flexible ANS. It means your body can efficiently switch between the energetic “fight-or-flight” (sympathetic) mode and the calming “rest-and-digest” (parasympathetic) mode. This flexibility is a hallmark of good recovery, fitness, and stress resilience.
Low HRV: Suggests a less flexible ANS, often stuck in a state of higher sympathetic tone (stress). It is associated with overtraining, chronic stress, fatigue, illness, and poor recovery.
HRV During Sleep: Your Purest Reading
HRV can be measured throughout the day, but the reading taken during deep sleep is considered the gold standard. During this phase, external distractions are minimized, providing the clearest signal of your physiological state without the “noise” of daily activity and thoughts.
Your HRV naturally fluctuates nightly. It will be lower after days of intense physical or mental stress and higher after days of good rest and relaxation.
The key is to identify your personal baseline range over several weeks of normal training and lifestyle, and then watch for significant deviations.
Using HRV Data Proactively
HRV is not a score to “beat” every day. It’s a feedback tool:
A Sudden Drop: If your HRV drops significantly below your baseline for 2-3 consecutive nights, it’s a strong indicator that your body is struggling to recover. This is a signal to consider a lighter workout, an early night, or extra focus on nutrition and hydration.
A Sustained Low Trend: A consistently low HRV over weeks might point to underlying issues like chronic stress, inadequate sleep, or an imbalanced training load.
Personal, Not Comparative: HRV is highly individual. Comparing your number to someone else’s is meaningless. A very fit person might have a lower HRV than a moderately active one due to genetic differences. Your own trends are what matter.
By paying attention to your nocturnal HRV, you move from guessing how you feel to knowing how recovered you are. It allows you to tailor your daily activity to your body’s actual capacity, helping to prevent burnout and overtraining. This science-backed approach to personal optimization reflects the vision and values behind modern wellness technology.
Breathing Rate: The Silent Rhythm of Sleep
Your respiratory rate—the number of breaths you take per minute—is a vital sign that remains remarkably stable in healthy individuals during sleep. Monitoring its average and detecting anomalies can provide early clues about sleep quality and potential health issues.
The Baseline of Nightly Breath
For a healthy adult at rest, a normal sleeping respiratory rate typically falls between 10 and 22 breaths per minute. Like heart rate, it should be lower during sleep than during wakeful rest, reflecting the body’s calm, parasympathetic state.
This metric is often averaged over the entire night. A stable, low-average rate (e.g., 12-16 breaths per minute) is a sign of efficient, relaxed breathing and good sleep.
Significant deviations from your personal norm can be informative.
What Changes in Breathing Rate Can Signal
Elevated Average Rate: A consistently higher-than-normal sleeping respiratory rate can be a subtle sign of several things:
Physical Stress: Your body may be working harder to recover from illness, infection, or intense physical exertion.
Respiratory Issues: Allergies, mild asthma, or environmental irritants can increase breathing effort.
Sleep Disruption: Even if you don’t remember waking up, fragmented sleep can cause periods of faster breathing.
Detection of Breathing Irregularities: Advanced wearables, particularly some smart rings and watches, can detect significant breathing disturbances. For instance, they may flag episodes where your breathing becomes very shallow or pauses altogether—potential indicators of sleep apnea. It’s crucial to understand that these consumer devices are screening tools, not diagnostic instruments. They can empower you to seek a professional evaluation from a sleep specialist, who can conduct a formal sleep study (polysomnography) for a definitive diagnosis.
The Value of Passive Monitoring
The power of tracking respiratory rate lies in its passivity and continuity. A doctor can measure it in a clinic once, but your wearable measures it every night, establishing a rich baseline. This allows you to see:
The impact of lifestyle changes (e.g., does using an air purifier or a different pillow lower your rate?).
How respiratory rate correlates with other metrics like HRV and deep sleep.
Long-term trends that might warrant a professional conversation.
Paying attention to this quiet rhythm of the night adds another layer of understanding to your overall sleep health picture, moving you closer to a truly holistic view of your recovery.
Skin Temperature: The Body’s Thermostat Tells a Story
Your core body temperature follows a circadian rhythm, naturally dipping in the evening to initiate sleep and rising in the morning to promote wakefulness. Skin temperature, as measured by the sensors on a smart ring, is a proxy for these changes and a sensitive indicator of internal shifts.
The Normal Nocturnal Curve
As you fall asleep, blood vessels in your skin dilate (vasodilation) to release heat, causing a slight increase in skin temperature at the extremities (like your finger). As sleep progresses, your core temperature continues to drop, which is essential for maintaining deep, consolidated sleep.
A smart ring tracks this relative change from your personal baseline, established over weeks of wear.
A smooth, predictable temperature curve throughout the night is a hallmark of stable, high-quality sleep.
Interpreting Deviations from Your Baseline
Changes in your nocturnal temperature trend can be highly informative:
A Sustained Elevation: If your skin temperature trend is consistently higher than your baseline for multiple nights, it is one of the earliest and most reliable signs that your body is fighting an illness or infection, even before you feel symptoms. It can also be influenced by hormonal fluctuations during a woman’s menstrual cycle.
A Disrupted Curve: A jagged or irregular temperature graph, with spikes and drops, often corresponds to sleep fragmentation. Awakenings and periods of light sleep can cause temperature fluctuations, breaking the smooth cooling pattern.
Environmental Influence: An overly warm sleeping environment can blunt your body’s natural cooling process, leading to more restless sleep and less deep sleep. Your temperature data can confirm whether your room is optimally cool (typically around 65°F or 18°C).
From Data to Action
Temperature data is powerful because it’s physiological, not subjective. If your ring shows a elevated temperature trend:
You might decide to prioritize rest, hydrate well, and avoid strenuous activity to help your immune system.
You can experiment with adjusting your bedroom thermostat or bedding to see if it creates a smoother, more optimal cooling curve on your graph.
This metric exemplifies the proactive potential of continuous monitoring. It turns your wearable into a early-warning system, giving you a data-backed reason to slow down and care for yourself before a minor issue becomes a full-blown problem. Understanding these subtle biological signals is part of the fascinating journey and story behind advanced health tracking.
The Sleep Score: Your Nightly Performance Grade
The Sleep Score (sometimes called a Sleep Quality Score) is a single, composite number—often between 0 and 100—that most sleep tracking platforms provide. It serves as an instant, high-level assessment of your night. While the specific algorithms are proprietary, they generally weigh several key metrics we've already explored:
How Your Score is Calculated
Although the exact formula varies by device and platform, a typical Sleep Score might be derived from a combination of:
Sleep Duration (Total Sleep Time): This is usually the heaviest weighted factor. Did you meet your personal sleep need?
Sleep Structure (Sleep Stages): The balance and sufficiency of deep sleep and REM sleep contribute significantly.
Sleep Continuity (Efficiency & Awake Time): How consolidated was your sleep? High fragmentation lowers the score.
Timing (Sleep Latency & Consistency): Falling asleep reasonably quickly and sleeping during your body's natural circadian window positively impacts the score.
For example, a night with 8 hours in bed, high efficiency, a healthy balance of deep and REM sleep, and minimal awakenings would likely generate a score in the "Excellent" range (often 85+). A night with sufficient time but frequent disruptions and low deep sleep might result in a "Fair" score (e.g., 70-79).
How to Use (and Not Abuse) Your Sleep Score
The Sleep Score is designed as a useful summary, but it’s crucial to use it wisely:
It’s a Summary, Not a Diagnosis: Don't fixate on the absolute number. Instead, use it as a starting point. A lower-than-usual score is your cue to drill down into the component metrics to understand why. Did your heart rate not dip? Was your REM sleep low? The score tells you that something was off; the underlying data tells you what.
Track Trends, Not Dailies: Your sleep will naturally vary. A single night with a score of 72 is not a crisis. However, a downward trend over a week or a consistently low average is a meaningful signal that warrants attention to your habits, stress, or environment.
Avoid "Gamifying" Your Rest: The goal is restorative sleep, not a high score. Avoid behaviors that might artificially inflate your score at the expense of true rest, like forcing yourself to stay in bed longer when you're awake just to boost "duration."
Think of your Sleep Score as your nightly report card. It gives you a quick sense of how the night went, but to truly improve, you need to read the teacher's comments—the detailed metrics beneath it. For a deeper understanding of how these algorithms work to support your wellness, you can learn more about the science behind our approach.
The Readiness/Recovery Score: Translating Sleep into Daytime Capacity
While the Sleep Score looks backward at your night, the Readiness Score (or Recovery Score) looks forward at your day. This next-generation metric answers a critical question: "Based on how I recovered last night, how prepared is my body and nervous system for today's physical and mental demands?"
The Physiology Behind Readiness
A Readiness Score is a more advanced composite that typically incorporates:
Sleep Data: The quality and structure of your previous night's sleep.
Cardiovascular Data: Your resting heart rate and, most importantly, your Heart Rate Variability (HRV). HRV is often the star player here, as it's the clearest objective indicator of autonomic nervous system recovery.
Activity Balance: Some scores consider your recent activity load, assessing whether you've had adequate recovery from prior exertion.
Other Biomarkers: Metrics like skin temperature trends and respiratory rate can feed into the algorithm, especially to detect signs of illness or elevated stress.
A high Readiness Score suggests your body has recovered well, your stress load is low, and you are physiologically primed for a challenging workout, a demanding cognitive task, or a busy day. A low score is a recommendation from your body to prioritize rest, choose lighter activity, manage stress, and focus on recovery-supportive habits.
Making Readiness Data Actionable
This is where data transforms into powerful daily wisdom. Here’s how to integrate a Readiness Score into your routine:
Check It First Thing: Make it part of your morning ritual, alongside your coffee or tea. Let it set the tone for your day’s intentions.
Let It Guide Your Training: This is a cornerstone of heart-rate variability training. A high score? Go for that intense session or personal record attempt. A low score? Opt for a gentle walk, yoga, mobility work, or a complete rest day. This practice helps prevent overtraining and injury.
Let It Guide Your Pace: Even if you don't exercise, a low score can be a reminder to take things slower, schedule fewer meetings, practice mindfulness, or go to bed earlier that night.
By honoring your Readiness Score, you learn to collaborate with your body rather than fight against it. You stop guessing if you’re “ready” and start knowing. This alignment between your daily choices and your physiological state is a profound step toward sustainable health and performance. To see how real people have used this data to transform their routines, you can explore authentic user experiences in our testimonials.
Putting It All Together: Diagnosing Common Sleep Patterns
With a firm grasp on individual metrics and composite scores, you can now start playing detective. Your sleep data forms recognizable patterns that point to specific root causes. Here are three common archetypes and what they signify.
The "Restless & Inefficient" Pattern
Signature Data:
Low Sleep Efficiency (consistently below 80%)
High Awake Time and/or frequent Wake-Ups
Elevated or Fluctuating Sleeping Heart Rate
Possibly lower Deep Sleep
What It Suggests: This pattern screams sleep fragmentation. Your sleep is choppy and shallow. Common causes include:
Environmental Disruptions: Noise, light, an uncomfortable mattress, or a room temperature that's too warm.
Lifestyle Factors: Alcohol consumption (which causes rebound awakenings), caffeine too late, or a large meal before bed.
Health Considerations: Sleep apnea (pauses in breathing followed by micro-arousals), restless leg syndrome, or chronic pain.
Action Plan: Focus on consolidation. Improve your sleep environment (cool, dark, and quiet), strictly avoid alcohol before bed, and consider tracking these changes to see their direct impact on your efficiency metric. If symptoms persist, especially with snoring or witnessed breathing pauses, discuss the data with a doctor.
The "Short & Stressed" Pattern
Signature Data:
Insufficient Total Sleep Time (consistently under 7 hours)
High Sleep Latency (trouble falling asleep)
Low or Flattened Heart Rate Dip
Low HRV Trend
What It Suggests: This pattern points to hyperarousal of the nervous system, both cognitive and physical. Stress is preventing sleep onset and dampening recovery.
Cognitive Overload: An overactive mind fueled by anxiety, worry, or excessive screen time before bed.
Schedule & Behavior: A mismatched circadian rhythm due to irregular bedtimes or "revenge bedtime procrastination" (staying up late to reclaim personal time).
Sympathetic Dominance: Chronic stress is keeping your body in a heightened state, visible in the poor heart rate and HRV data.
Action Plan: Focus on wind-down and stress management. Implement a strict, screen-free pre-bed routine. Practice relaxation techniques like meditation or deep breathing. Most critically, protect your sleep schedule and aim for an earlier bedtime to increase duration. Watching your HRV respond to these changes can be highly motivating. For more structured guidance on building these habits, our blog offers a wealth of related resources.
T
he "Long But Unrefreshing" Pattern
Signature Data:
Adequate or Long Total Sleep Time (8+ hours)
But low Sleep Score and feelings of daytime fatigue
Imbalanced Sleep Stages (e.g., excessively high percentage of Light Sleep, very low Deep or REM Sleep)
Possibly unremarkable heart rate/HRV data
What It Suggests: You’re spending time in bed, but not getting the quality of sleep you need. This can be frustrating because the effort seems right, but the result is wrong.
Poor Sleep Architecture: You may be spending too much time in light sleep and not enough in restorative deep and REM stages.
Underlying Sleep Disorders: Conditions like sleep apnea or periodic limb movement disorder can severely fragment sleep and disrupt stages without causing long, memorable awakenings.
Medication or Substance Effects: Some medications, and even long-term use of certain sleep aids, can suppress deep or REM sleep.
Action Plan: Focus on sleep quality over mere quantity. Since the time in bed is there, the goal is to improve its structure. Rule out environmental disruptions first. If the pattern persists, a Readiness Score that remains low despite long sleep is a red flag. This data is incredibly valuable to bring to a healthcare provider or sleep specialist for further evaluation.
Creating Your Personal Sleep Improvement Plan: A Step-by-Step Framework
Knowledge is only power if you apply it. This framework turns insights from your data into a concrete, personalized action plan.
Step 1: Establish Your Baseline (2-3 Weeks)
Do not try to change everything at once. Start by simply wearing your tracker consistently and observing.
Note your averages: What is your typical Sleep Score? Total Sleep Time? Sleep Efficiency? HRV?
Observe natural patterns: How does your data change after a stressful day, a workout, or a weekend?
Step 2: Identify Your Primary Lever (The "One Thing")
Based on your dominant pattern from the section above, choose one key metric to improve.
If efficiency is low: Your lever is consolidation. Your goal is to reduce awake time.
If duration is short: Your lever is schedule. Your goal is an earlier bedtime.
If latency is high: Your lever is wind-down. Your goal is to calm your mind before bed.
If HRV is low/recovery is poor: Your lever is stress management. Your goal is to incorporate daily relaxation.
Step 3: Design a Focused Experiment (2-3 Weeks)
Implement one or two changes specifically targeted at your chosen lever.
Lever: Consolidation? Experiment by: 1) Removing alcohol for 2 weeks, and 2) Using a white noise machine.
Lever: Schedule? Experiment by: 1) Moving your bedtime 20 minutes earlier every 3 days until you hit your target, and 2) Setting a consistent alarm.
Lever: Wind-down? Experiment by: 1) Instituting a 60-minute, screen-free pre-sleep routine, and 2) Using a meditation app.
Lever: Stress Management? Experiment by: 1) Adding 10 minutes of breathwork in the morning, and 2) Taking a 15-minute walk in nature.
Step 4: Measure, Analyze, and Iterate
This is the critical data-driven loop.
Watch the relevant metrics: Did your experimental changes move the needle on your target lever? Did your Sleep Score or Readiness Score improve?
Note secondary effects: Did improving efficiency also increase your deep sleep? Did an earlier bedtime improve your HRV?
Adjust and continue: If it worked, make it a habit. If it didn’t, try a different variable. Move on to your next lever.
By following this framework, you become a scientist of your own sleep. You move away from generic tips and toward personalized, verified strategies that work for your unique biology and life. This process of continuous learning and adaptation is at the heart of the modern, proactive wellness journey.
Beyond the Night: How Daytime Habits Create Nightly Data
Your sleep data is not created in a vacuum. It is the end product of everything you do during the preceding 16 hours. To truly master your sleep, you must widen the lens and see the entire daily cycle.
The Sunlight Anchor
Morning sunlight exposure is the most powerful signal to set your circadian rhythm. It suppresses melatonin, boosts cortisol (in a healthy way), and starts the timer for its release about 14 hours later. A lack of morning light can lead to a delayed or weakened rhythm, making it harder to fall asleep at night.
The Exercise Equation
Physical activity is fantastic for sleep, but timing matters.
Morning/Afternoon Exercise: Strengthens the circadian drive and deepens sleep.
Late-Evening Intense Exercise: Can raise core body temperature and stimulate the nervous system too close to bedtime, potentially disrupting sleep onset for some people. If you exercise late, monitor your sleep latency and heart rate dip to see how you personally respond.
Nutrition & Substances
What you consume acts as direct input to your sleep system.
Caffeine: Has a half-life of 5-6 hours. For better sleep, consider a caffeine curfew by early afternoon.
Alcohol: It’s a sedative, not a sleep aid. It suppresses REM sleep and causes rebound awakenings, often visible in your Awake Time metric in the second half of the night.
Food Timing: A large, heavy meal right before bed forces your digestive system to work, which can raise body temperature and disrupt sleep. A light snack is usually fine.
The Stress Tally
Unmanaged daytime stress accumulates, leading to elevated cortisol levels that can persist into the evening. This directly antagonizes the release of melatonin and keeps your nervous system aroused. This is why a stressful day often shows up as high sleep latency, a high sleeping heart rate, and low HRV that night. Building in daily stress resets—like short walks, mindfulness breaks, or disconnecting from work—pays a direct dividend in your sleep data.
Understanding these connections turns your entire day into a sleep optimization opportunity. Each healthy choice is an investment that will mature in the form of better data and better feelings the following morning.
Sleep Tracking Metrics Decoded: What Each Number Means (Final)
In the previous sections, we mastered the language of sleep data—from the basic building blocks of duration and stages to the sophisticated synthesis of Readiness Scores. You learned how to diagnose patterns and build a personal sleep improvement plan based on your unique physiology. This knowledge transforms you from a passive user into an informed architect of your own rest.
Now, we look toward the horizon. What does the future of sleep technology hold, and how will it deepen our understanding? Furthermore, how do these principles apply to the unique challenges faced by athletes, shift workers, and new parents? In this final section, we will explore the cutting edge of sleep tracking, address specialized needs, and solidify a sustainable philosophy for using this technology not as a source of anxiety, but as a lifelong tool for empowerment and well-being. This is where data meets wisdom.
The Cutting Edge: Emerging Metrics and Future Technology
The evolution of sleep tracking is moving beyond heart rate and movement toward direct measurement of the brain and nervous system. This next wave promises even greater precision and personalization.
From Movement to Brainwaves: The Rise of Wearable EEG
Current consumer devices primarily use actigraphy (movement) and photoplethysmography (PPG - optical heart rate) to infer sleep stages. The next frontier is electroencephalography (EEG), which measures the brain's electrical activity directly.
Early-adopter headbands and wearable patches with dry EEG sensors are already on the market. What this means for you:
True Sleep Stage Detection: Instead of an algorithm's educated guess, you get a direct readout of your brainwaves, offering near-clinical accuracy in distinguishing Light, Deep, and REM sleep.
Sleep Onset Precision: Pinpoint the exact moment you transition from wakefulness to sleep, removing estimation from Sleep Latency.
"Sleep Fingerprinting": Research suggests individual EEG patterns may reveal insights into cognitive health, memory consolidation efficiency, and even early signs of neurological conditions. While not a diagnostic tool, tracking your own baseline EEG over years could provide unprecedented personal health insights.
Precision Temperature and Micro-Environment Sensing
While current devices track relative skin temperature trends, future sensors aim for medical-grade accuracy and new measurement sites.
Core Temperature Proxies: Advanced algorithms combining finger temperature, heart rate, and movement may provide a reliable estimate of core body temperature's circadian rhythm, a master regulator of sleep.
Micro-Environment Monitoring: Future devices or paired sensors may actively measure the temperature, humidity, light levels, and noise in your immediate sleeping environment. Your app could then correlate a night of poor Sleep Efficiency directly with a spike in ambient noise at 2 a.m. or a room temperature that crept above 72°F.
Biomarkers in Breath and Sweat
Research is exploring non-invasive ways to detect biomarkers that signal sleep quality and health.
Respiratory Analysis: More advanced analysis of breathing rate variability could provide clues about nervous system balance, similar to HRV.
Galvanic Skin Response (GSR): This measures tiny changes in sweat gland activity, which is a direct indicator of sympathetic nervous system ("fight-or-flight") arousal. Integrated into a ring or watch, it could quantify nighttime stress episodes with high sensitivity.
These advancements will make sleep data richer and more actionable. However, the core principles you've learned—tracking trends, seeking root causes, and focusing on holistic habits—will remain essential for interpreting this coming wave of information. Staying informed on these developments is part of engaging with the future of wellness; you can follow our blog for ongoing updates on these evolving technologies.
Special Populations: Tailoring Sleep Tracking to Your Life
Sleep needs and challenges are not one-size-fits-all. Here’s how to contextualize sleep data for specific lifestyles.
For the Athlete and Fitness Enthusiast
For athletes, sleep is the primary performance-enhancing drug. Data tracking here is mission-critical.
Key Metric: HRV & Readiness: This is your non-negotiable guide. A low Readiness Score or a significant drop in HRV is a direct order to modify training. Pushing through leads to overtraining, injury, and illness. Use it to periodize your rest.
Deep Sleep as a Repair Metric: Track your Deep Sleep duration and consistency. It directly correlates with physical repair, muscle growth, and hormone regulation. Notice how it increases during recovery weeks or decreases during high-volume training blocks.
The Impact of Late Training: Monitor your Sleep Latency and Sleep Efficiency closely if you train in the evening. If they suffer, consider shifting intense sessions earlier or implementing a more aggressive cooling and wind-down routine post-workout.
For the Shift Worker and Chronotype Explorer
Those who work nights or have a strong natural tendency toward being a "night owl" (a late chronotype) face a fundamental conflict with the conventional 9-5 world.
Focus on Consistency, Not Timing: Your goal is to anchor your sleep to your schedule. Use the data to find the most consistent 8-hour sleep window you can maintain, even if it's 9 AM to 5 PM. Protect this window fiercely. Your Sleep Score within this window is your measure of success.
Light Management is Data-Worthy: Since light is your primary circadian cue, your efforts to block daylight before sleep (blackout curtains, blue-light blockers) and seek bright light upon waking (light therapy lamp) are direct interventions. Track how these practices affect your Sleep Latency and morning alertness.
Understand the Trade-offs: Even with perfect habits, shift work sleep is often less efficient and restorative than night-time sleep. Your data may show slightly lower Sleep Efficiency or less Deep Sleep. This isn't a personal failing—it's a biological reality. The data helps you quantify the impact and reminds you to prioritize recovery even more.
For New Parents and Caregivers
This phase is about survival and managing extremes. Perfection is off the table; insight is still invaluable.
Reframe Your Metrics: Toss out the standard benchmarks. Your Total Sleep Time will be a sum of chunks. Your Sleep Efficiency will be low due to necessary awakenings. That's okay.
Track Your Own Recovery in Snippets: Focus on what you can control: your own Sleep Latency. When you get a chance to sleep, how quickly can you fall asleep? Practice wind-down techniques for these moments. Also, watch your Resting Heart Rate trend; a creeping elevation over weeks is a hard signal that you need to ask for more support or grab rest whenever possible.
Use Data for Co-Parent Coordination: If both partners wear trackers, data can facilitate teamwork. The parent with a higher Readiness Score or more Deep Sleep the night before might take the morning shift. It turns sleep into a shared resource to be managed equitably.
In all these cases, the wearable is not a judge; it's a biometric translator. It turns the unique pressures of your life into objective data, allowing you to make smarter, more compassionate choices for your health within your real-world constraints. The story of modern wellness technology is about meeting people in the reality of their lives, not an idealized version of it.
Avoiding Data Anxiety: Cultivating a Healthy Relationship with Your Tracker
An ironic side effect of sleep tracking can be orthosomnia—an unhealthy preoccupation with perfect sleep data that ironically increases anxiety and worsens sleep. Here’s how to harness the power of data without falling into the trap.
Recognize the Warning Signs
Your tracker should be a tool for better living, not a source of daily stress. Be mindful if you:
Feel dread or anxiety when checking your morning score.
Make rigid, unsustainable life choices solely to "game" your numbers.
Ignore how you actually feel in favor of what the data says.
Experience increased sleep effort and frustration, which is counterproductive.
Adopt a Balanced Data Philosophy
Prioritize Subjective Feelings: Always lead with "How do I feel?" before consulting the data. If you feel great with a Sleep Score of 75, celebrate that. The data is there to explain bad feelings, not to invalidate good ones.
Embrace the 80/20 Rule: You don't need a perfect 100 every night. Aim for consistency within a range that supports how you want to feel. Five "good enough" nights a week are better than one perfect night and four stressful attempts at perfection.
Take Regular Data Holidays: Consider taking the ring off for a weekend, a vacation, or one night a week. This breaks the cycle of constant monitoring and reconnects you with your body's innate cues. You'll often find your sleep is fine without it, which is a liberating realization.
Use Data for Compassion, Not Criticism
When you see a poor night of data, change your internal dialogue. Instead of: "I failed last night," try: "My body was telling me it needed more support. What was different yesterday?" Frame it as curiosity, not judgment. This shift turns data from a report card into a collaborative feedback system.
The ultimate goal is to internalize the lessons the data teaches you so that you eventually need the device less. You learn what good sleep feels like in your body, and you learn the habits that reliably get you there. This is the journey from external tracking to internal wisdom. For support on this journey, our community and FAQ resources are always available.
The Long-Term Vision: Sleep Data as a Pillar of Lifelong Health
Looking beyond nightly optimization, consistent sleep tracking provides a unique, long-term asset: a longitudinal health record.
Establishing Your Personal Baselines
Over months and years, you establish what "normal" looks like for you. This is far more valuable than population averages. You'll know:
Your personal HRV range.
Your typical Deep Sleep percentage.
Your normal sleeping respiratory rate.
Detecting Meaningful Deviations
With solid baselines established, you can detect subtle, long-term shifts that may signal changes in health.
A gradual, sustained increase in your resting heart rate over months could be a prompt to assess cardio fitness and stress.
A notable change in your temperature rhythm or sleep architecture as you age provides concrete information to discuss with a healthcare provider during regular check-ups.
Tracking how your sleep responds to life events, menopause, or new medications provides powerful personal evidence to guide decisions.
Integrating into a Holistic Health Picture
Sleep data is not a standalone metric. It is one vital stream in a river of health data that includes nutrition, activity, mindfulness, and medical check-ups. The future of wellness lies in integrating these streams to see the full picture. For instance, seeing how a week of poor sleep correlates with higher blood glucose readings or worse workout performance creates undeniable motivation for change.
By faithfully collecting this data, you are building a powerful narrative of your health over time—a narrative that empowers you to be proactive, to advocate for yourself with clarity, and to make daily choices that compound into a lifetime of vitality. This proactive, data-informed approach to self-care is at the very heart of our company's mission and vision.
Conclusion: From Numbers to Wisdom
We began this journey with a simple frustration: waking up tired, armed with nothing but a vague feeling and a number of hours. We end it with a profound new literacy.
You now understand that Sleep Efficiency reveals the stealthy cost of fragmentation, that Heart Rate Variability whispers the truth about your recovery, and that Skin Temperature can sound an early alarm before you feel ill. You've learned to see beyond the Sleep Score to the story beneath and to let the Readiness Score guide your day with biological intelligence.
More importantly, you've gained a framework for action. You know how to diagnose the "Restless & Inefficient" night, to run a personal sleep experiment, and to tailor this knowledge to your life—whether you're an athlete, a shift worker, or a parent in the thick of it.
Remember, the goal was never to achieve a perfect score every night. The goal was to gain understanding. To replace mystery with insight, and guesswork with strategy. To build a collaborative relationship with your own body, using data as your shared language.
So, look at your next sleep report not as a judgment, but as a conversation. Your body is speaking. Thanks to the knowledge you now possess, you are finally equipped to listen, understand, and respond. Here's to your next night of truly intelligent, restorative sleep, and to all the vibrant, well-recovered days that follow.
Your journey to mastering your sleep is just beginning. For more personalized insights, deeper dives into wellness science, and to join a community focused on proactive health, we invite you to explore our complete platform and continue the conversation.
Potential directions for expansion:
Comparative Analysis of Wearable Technologies - Deep dive into how different devices (smart rings vs. watches vs. headbands) measure sleep metrics, their strengths and weaknesses
Sleep Disorders Deep Dive - More detailed analysis of how specific sleep disorders (sleep apnea, insomnia, restless leg syndrome) manifest in tracking data
Sleep Optimization Toolkit - A practical guide with specific protocols for improving each metric, including meal timing, light exposure protocols, and supplementation
Case Studies - Analysis of real (anonymized) sleep data patterns from different user types with troubleshooting narratives
The Science of Napping - How to track, optimize, and strategically use naps based on sleep stage data and circadian timing
Sleep and Aging - How sleep architecture changes through decades and how to adjust expectations and optimization strategies accordingly
The Limitations of Consumer-Grade Stage Tracking
First, it's crucial to understand what your current wearable is—and isn't—measuring. Most consumer devices (smart rings, watches, and under-mattress sensors) use a combination of actigraphy (movement) and photoplethysmography (PPG - blood volume pulses for heart rate) to infer sleep stages through sophisticated algorithms.
While these algorithms have improved dramatically and provide valuable trend data, they are making educated guesses based on proxies. They cannot directly measure brain activity. This leads to several limitations:
Stage Misclassification: Brief awakenings, periods of quiet rest, and certain sleep disorders can be misclassified as light sleep. The boundary between deep sleep and REM sleep, which can have similar heart rate and movement profiles, is particularly challenging to distinguish accurately without brainwave data.
Lack of Granularity: You see "Deep Sleep" as a block, but not the continuity or intensity of that deep sleep. Two nights with 60 minutes of deep sleep are not equal if one consists of a single, solid hour and the other is fragmented into six 10-minute chunks constantly interrupted by micro-arousals.
Missing the "How" and "Why": Your device can tell you your REM sleep was low, but not why. Was it suppressed by alcohol? Disrupted by sleep apnea events? Shortened because you woke up early? The root cause often requires looking at more precise biological signals.
Recognizing these limitations isn't a criticism of the technology—it's an acknowledgment of its purpose. Consumer trackers are excellent for trend analysis and behavioral guidance. To delve into the architectural details, we must look to more advanced tools and the principles they measure.
Core Sleep Architecture Principles: Cycles, Progression, and Ultradian Rhythms
Beyond the simple percentage breakdown of stages lies the concept of sleep architecture—the organized, cyclical structure of a night's sleep.
The 90-Minute Ultradian Rhythm
Sleep does not randomly bounce between stages. It follows a predictable ultradian rhythm, with each complete cycle lasting approximately 90 to 120 minutes in healthy adults. A typical, well-architected night consists of 4 to 6 of these cycles.
Cycle 1: Begins with a descent from wakefulness through light sleep (N1, N2) into deep sleep (N3). REM sleep is usually brief or absent in this first cycle. This is when the body prioritizes physical restoration.
Cycles 2 & 3: These often contain the highest proportion of deep sleep. The duration of REM periods begins to increase toward the end of each cycle.
Cycles 4+: In the second half of the night, deep sleep diminishes and often disappears, while REM sleep periods become progressively longer and more intense. This is when the brain prioritizes memory consolidation, emotional processing, and creativity.
Why This Matters for You: If you consistently cut your sleep short (e.g., getting only 5 hours, or about 3-4 cycles), you are disproportionately robbing yourself of the extended REM sleep that dominates later cycles. This can manifest as brain fog, emotional irritability, and poor memory consolidation, even if your "Deep Sleep" metric looks fine. Your tracker's sleep stage graph should show this evolution—if every cycle looks identical, it may indicate an algorithm limitation or a disruption in normal progression.
Sleep Maintenance and the "Sleep Gate"
The transition between cycles is not always seamless. Brief awakenings (often too short to remember) are normal at the end of a cycle at the "sleep gate." However, the ability to quickly descend back into sleep is key.
Healthy Architecture: A slight increase in movement or heart rate at the ~90-minute mark, followed by a smooth return to light and then deep sleep.
Disrupted Architecture: A full awakening, prolonged period of wakefulness, or an immediate jump into a very light sleep stage without deeper progression. This fragmentation is what truly degrades sleep quality, as it prevents the completion of full, restorative cycles.
On your data, this may appear as clusters of "Awake" or "Light Sleep" periods at roughly 90-minute intervals. It’s a more specific pattern than random wake-ups throughout the night.
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