Learn

Sleep Score: Your Sleep in One Number

The first thing you see when opening Mellows is your sleep score — a 0–100 composite that distills complex sleep data into a single, easy-to-read result.

What Is a Personal Baseline?

Everyone's physiology and sleep needs are different. Seven hours of sleep is plenty for some, far too little for others. An HRV of 40 ms may be low for a 25-year-old athlete, yet perfectly normal for a 55-year-old desk worker.

Sleep Age: How old does your sleep look?

Your age keeps going up. Your sleep doesn't have to.

A Guide to Breathing Exercises

Breathing exercises are one of the most effective tools for calming your mind and regulating your nervous system. By consciously controlling your breath, you can shift your body between states of alertness and relaxation.

Recovery Score: How Well Did Your Body Recover Last Night

Sleep isn't just about being unconscious. Two people can sleep 7 hours and experience vastly different levels of recovery. The Recovery Score answers exactly this: how much did your body actually recover during sleep.

Aging Pace: what that gap means in speed

Sleep Age tells you how far your current sleep is from your actual age.

What's Ahead

Sleep Age tells you how far your sleep is from your actual age. Aging rate turns that gap into how fast your clock is running.

Bedtime Window: When Your Body Most Wants to Sleep

Many people assume there's one bedtime that's best for everyone, like "you must be asleep before 10 pm." But sleep science gives a more personal answer: the bedtime that suits you depends on your own biological rhythm, not a universal clock time.

Spatial Mix: Let Sound Surround You

An ordinary sleep sound is a single looping track: one stretch of rain, spread flat against your ears from start to finish. Spatial Mix is different. It's a multi-track spatial soundscape where you drag elements like rain, ocean waves, and insect song to different spots on a circular canvas, creating a sense of sound distributed all around you.

Sleep Stages Explained

Each night your brain cycles through multiple sleep stages, each serving a distinct restorative function. Understanding these stages helps you interpret what sleep quality truly means.

What Is Heart Rate Variability (HRV)?

Heart Rate Variability (HRV) measures the variation in time between consecutive heartbeats. Contrary to common belief, a higher HRV is generally better — it reflects your autonomic nervous system's ability to adapt and regulate.

Sleep Heart Rate: Your Nighttime Cardiovascular Barometer

When you're awake, heart rate is influenced by activity, emotions, and caffeine, making it hard to gauge your heart's true state. During sleep, your body reaches its lowest metabolic level, producing cleaner heart rate data — which is why sleep heart rate is an ideal window into cardiovascular health.

Blood Oxygen: A Window into Breathing Quality During Sleep

Blood oxygen saturation (SpO2) measures the percentage of oxygen carried by hemoglobin in your blood. With each breath, your lungs load oxygen onto hemoglobin, which then delivers it to tissues throughout your body. SpO2 is the number that reflects how efficiently this process works.

Wrist Temperature: Your Body's Hidden Signal

Wrist temperature is a sleep metric available on Apple Watch Series 8 and later. It measures how your overnight skin surface temperature deviates from your personal baseline, revealing subtle changes happening inside your body.

Sleep Efficiency: How Well You Use Your Time in Bed

Sleep efficiency is a simple yet powerful metric: time actually asleep ÷ total time in bed × 100%.

Sleep Consistency: The Underrated Sleep Superpower

You probably already know that getting 7-8 hours matters. But there's an equally important factor that often gets overlooked: whether you go to bed and wake up at roughly the same time each day.

Sleep Duration: How Much Sleep Do You Actually Need

"Get eight hours" is the most repeated piece of sleep advice, and one of the most misleading. Real sleep need is a range, and it varies from person to person.

Sleep Continuity: Why "Enough Sleep" Isn't the Same as "Good Sleep"

Two people each sleep 7 hours. One rests soundly all night; the other wakes five or six times. Same duration, completely different restoration. The difference is sleep continuity: whether your sleep gets interrupted again and again.

Sleep Latency: The Stretch Between Lying Down and Falling Asleep

Lights off, eyes closed, and then what? The time between deciding to sleep and actually falling asleep is called sleep latency. This unassuming metric holds a surprising amount of information about your sleep state.

Respiratory Rate: The Quietest Health Signal in Your Sleep

While awake, you can consciously breathe deeply, hold your breath, adjust your rhythm. But the moment you fall asleep, breathing is handed entirely to your autonomic nervous system. That's exactly why respiratory rate during sleep is such an honest signal: it can't be influenced by will, so it reflects your body's true state.

Caffeine and Sleep: It Lingers Longer Than You Think

Most people know that drinking coffee before bed hurts sleep. Far fewer realize that the latte you had at 2 PM may still be affecting your sleep quality at 11 PM.

Exercise and Sleep: A Two-Way Virtuous Cycle

Exercise is one of the most effective non-pharmacological ways to improve sleep. In turn, good sleep enhances exercise performance. Understanding this bidirectional relationship helps you build truly sustainable healthy habits.