Heart Rate During Sleep: Stage-by-Stage Guide
Your heart rate changes significantly across sleep stages — reaching its lowest point during N3 deep sleep and showing irregular, sometimes elevated rates during REM. This page explains what is normal at each stage, the cardiovascular significance of the nocturnal dip, and how accurately your wearable captures sleep HR data.
Educational Information — Not a Substitute for Medical Evaluation
Heart rate data is medical data. The ranges on this page represent population norms and general guidance only. Individual variation is significant and influenced by age, fitness level, medications, and underlying health conditions. If your wearable shows values consistently outside the ranges described, or if you experience symptoms such as palpitations, chest discomfort, or breathlessness during the night, discuss this with your GP. Do not use this page to self-diagnose cardiac conditions.
Heart Rate by Sleep Stage: Normal Ranges
Most sleep guides report only overall resting heart rate. This table provides the stage-by-stage breakdown — the more clinically meaningful picture. Note that N3 deep sleep is associated with the lowest heart rate and blood pressure of the entire 24-hour cycle, and REM is the most variable stage with the highest upper-range values of any sleep stage.
| Stage | Typical HR Range | Visual range | Characteristic | Key notes |
|---|---|---|---|---|
| Awake (resting) | 60-100 bpm | Daytime baseline | Individual varies substantially by fitness level, age, and medications | |
| N1 Light sleep | 55-85 bpm | Declining; 5-10% below waking | Brief stage; brief muscle twitches (hypnic jerks) may cause transient HR spikes | |
| N2 Core sleep | 50-80 bpm | Continued decline; steady and regular | Most time (~50% of sleep) spent here; highly regular HR rhythm | |
| N3 Deep sleep | 40-70 bpm | Lowest of night; nocturnal dip | Brief cardiac pauses up to ~2s are normal in N3; fit athletes may see 35-45 bpm | |
| REM sleep | 50-90+ bpm | Variable, irregular; emotionally driven | Can briefly reach waking-equivalent levels during intense dream states; wide variation is normal |
Ranges represent healthy adult norms. Lower end of N3 range applies primarily to trained endurance athletes. Upper end of REM range reflects brief spikes during emotionally intense dream content, not sustained elevated HR. Age, fitness, and medications significantly affect all ranges. Source: clinical polysomnography normative data.
Your Personal Sleep HR Estimator
Enter your resting daytime heart rate (measured after sitting quietly for 5 minutes, before getting up in the morning, or from your wearable’s resting HR reading) to see your personalised estimated sleep HR ranges per stage.
Your estimated sleep heart rate ranges
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Resting awake
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N1 Light sleep
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N2 Core sleep
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N3 Deep sleep
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REM sleep
Wearable Heart Rate Accuracy During Sleep
Unlike sleep stage classification — where wearables achieve approximately 70-78% accuracy compared to clinical polysomnography — heart rate measurement from photoplethysmography (PPG) optical sensors achieves approximately 90-95% accuracy during sleep for most modern devices. This means your wearable’s overnight HR data is meaningfully reliable and worth paying attention to for trend monitoring over time.
Sleep HR accuracy
PPG optical sensors measuring heart rate during sleep in validation studies against simultaneous ECG
Sleep stage accuracy
Movement and HR-based sleep stage classification compared to clinical polysomnographic EEG staging
The Nocturnal Dip: A Cardiovascular Health Marker
The nocturnal dip — a 10-20% reduction in heart rate and blood pressure during NREM sleep compared to daytime values — is one of the most clinically significant cardiovascular patterns measurable during sleep. Whether or not you show this dip is a meaningful predictor of cardiovascular risk, and modern wearables are beginning to allow long-term dip tracking in everyday life.
10-20%
Normal nocturnal HR dip
~25%
Adults are non-dippers
+30-40%
Elevated CVD risk in non-dippers
The nocturnal dip occurs as the autonomic nervous system shifts from sympathetic (fight-or-flight) to parasympathetic (rest-and-digest) dominance during NREM sleep. This shift lowers heart rate, reduces blood pressure, and decreases cardiac workload — providing a genuine physiological rest period for the cardiovascular system. Research consistently shows that adults who fail to show this dip (non-dippers) have significantly elevated cardiovascular disease risk compared to dippers, independent of other risk factors.
Dipper pattern (normal)
Heart rate and blood pressure fall 10-20% during NREM sleep relative to waking values. This is the normal, healthy pattern. The cardiovascular system gets a genuine rest period each night, reducing the cumulative mechanical stress on vessel walls and the heart. Dippers show lower long-term risk of hypertension, left ventricular hypertrophy, stroke, and coronary artery disease compared to non-dippers.
Non-dipper pattern (elevated risk)
Heart rate and blood pressure remain at or near daytime levels throughout sleep — no significant nocturnal rest for the cardiovascular system. Non-dipping is independently associated with 30-40% higher cardiovascular event risk. It is not a diagnosis but a risk marker. The most common treatable causes are sleep apnea (which causes repetitive arousal events that maintain sympathetic tone throughout the night) and poorly controlled hypertension.
Common causes of non-dipping
REM Sleep Heart Rate: Why It Spikes
REM sleep is the most physiologically active sleep stage for the cardiovascular system — and the most likely to produce readings on a wearable that look alarming but are completely normal. Understanding why REM heart rate is variable and sometimes elevated is important for correctly interpreting your overnight data.
Why REM Heart Rate Is Irregular and Sometimes Elevated
Emotional dream content
REM sleep is when the majority of vivid, emotionally rich dreaming occurs. The brain’s amygdala (emotional processing centre) is highly active during REM. The emotional content of dreams produces real autonomic responses — fear, excitement, or emotional intensity in a dream produces genuine sympathetic nervous system activation and consequent HR elevation. This is a normal and healthy feature of REM sleep, not a cardiac event.
Sympathetic activation during REM
Unlike NREM sleep — where parasympathetic dominance lowers HR systematically — REM sleep features variable and mixed autonomic tone. Sympathetic nervous system bursts during REM are normal and produce the brief HR spikes and irregular rhythm that wearables record. REM is sometimes described as a state of “internal activation” — the brain is nearly as active as during waking, which is reflected in the cardiovascular pattern.
REM in the second half of night
REM episodes lengthen across the night — the final REM periods before waking (typically 6-8 hours into sleep) are the longest and most intense. This means your wearable may show its most variable and elevated HR readings in the early morning hours. A brief HR elevation to 75-90 bpm at 5am on a wearable reading is almost certainly a normal late-night REM episode rather than a cardiovascular event.
Heart Rate Variability (HRV) During Sleep
Heart rate variability — the variation in time between successive heartbeats — is a separate but related metric to raw heart rate during sleep. Higher HRV during sleep is generally associated with better cardiovascular fitness and recovery status. Understanding how HRV relates to sleep stages provides additional context for wearable HRV readings.
HRV peaks in N3 deep sleep
HRV is highest during N3 deep sleep, reflecting peak parasympathetic nervous system dominance. High overnight HRV — particularly concentrated in N3 epochs — indicates effective autonomic recovery. This is why HRV-based recovery scores on wearables (Garmin Body Battery, Whoop Recovery, Oura Readiness) are heavily weighted by N3 sleep quality and duration.
HRV drops during REM sleep, reflecting the sympathetic activation that characterises the REM state. The irregular HR of REM comes with reduced HRV as the autonomic system responds to dream content. A low-HRV reading concentrated in the early morning hours (when REM is most frequent) is normal and does not indicate poor recovery — context of which sleep stage produced the reading matters.
HRV drops in REM
Using HRV for training decisions
Morning HRV readings (taken immediately on waking, before getting out of bed) correlate well with physiological recovery status and are used by many athletes to guide training load decisions. Consistently low morning HRV — below an individual’s own baseline trend — is a reliable early signal of overtraining, illness, or accumulated sleep debt before subjective symptoms emerge.
When to Discuss Your Sleep Heart Rate With Your GP
Discuss with your GP if your wearable consistently shows any of the following
These are not emergency criteria — they are reasons to raise at your next GP appointment or to book a review
Sleep Calculator
Calculate Your Optimal Sleep Cycle Timing
N3 deep sleep — where your heart rate dips lowest and cardiovascular recovery peaks — is concentrated in the first two sleep cycles. Waking at cycle end preserves this recovery window.
Open Sleep Cycle CalculatorFrequently Asked Questions
What is a normal heart rate while sleeping?
Normal sleeping heart rate varies significantly by stage and by individual. During N2 core sleep (which makes up approximately 50% of total sleep time), a healthy adult’s heart rate is typically 50-80 bpm — broadly consistent with what wearables report as “resting heart rate during sleep.” During N3 deep sleep, heart rate drops further to 40-70 bpm, with trained endurance athletes often showing 35-50 bpm at this stage. During REM sleep, heart rate is variable and irregular, ranging from 50-90+ bpm with brief spikes possible during emotionally intense dream states. Across the whole night, a typical healthy adult’s average sleeping HR is approximately 10-20% below their daytime resting HR. Consumer wearables measure overnight heart rate with approximately 90-95% accuracy using optical PPG sensors — significantly higher than their sleep stage classification accuracy of approximately 70-78%. Your wearable’s HR data is reliable and worth monitoring for trends over time, particularly the nocturnal dip pattern.
Is a low heart rate during sleep dangerous?
A low heart rate during sleep is normal and expected — and in fit individuals, very low N3 deep sleep heart rates are a sign of cardiovascular health, not a problem. The heart rate naturally falls during NREM sleep as the autonomic nervous system shifts to parasympathetic dominance. A trained endurance athlete seeing 38-45 bpm during deep sleep is showing a sign of good cardiovascular fitness, not bradycardia requiring concern. The threshold at which a low sleeping HR becomes clinically worth noting is approximately 40 bpm for non-athletes, particularly if combined with symptoms on waking such as dizziness, fatigue, or pre-syncope, or if the low HR persists throughout all sleep stages rather than just during N3. Heart rates below 35 bpm during sleep are uncommon even in elite athletes and warrant a GP discussion. The key question to ask about any low HR reading is: is this occurring specifically during N3 deep sleep (normal, expected, healthy), or is this the resting HR across all stages including light sleep and waking? A persistent resting HR of 45 bpm in a sedentary person during light sleep and wake is different from the same reading in an endurance athlete during N3.
