How much deep sleep do you need? There is no single target
Learn why there is no single deep-sleep target, how laboratory reference values differ from wearable estimates, and when a score needs more context first.
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Sleep Science
Plain-language explanations of sleep stages, timing and sleep measurement.
Sleep is easier to read about once the vocabulary is clear. These five guides explain sleep stages, REM and non-REM cycles, deep sleep and circadian timing in plain language, each drawn from public-health and research sources named on the page. They also describe how sleep is measured, and where a consumer estimate differs from a laboratory one.
Search all 35 guides and seven topic hubs.
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Browse every topicSleep Science guides.
5 guides, ordered by the question most people arrive with.
What is REM sleep? Its place in the sleep cycle
What is REM sleep? See where it sits in the sleep cycle, how it changes through the night, and why personal stage estimates need careful limits in context.
Stages of sleep: a map of REM and non-REM cycles
Map the stages of sleep, see how REM and non-REM alternate, and learn why a population cycle description is not a personal stage target for one person.
What is circadian rhythm? A guide to daily timing
What is circadian rhythm? Learn how roughly 24-hour patterns, light and darkness, the brain, and melatonin relate without self-diagnosing a disorder at home.
The importance of sleep shows up in everyday tasks
Understand the importance of sleep through bounded effects on attention, learning, memory, decisions, reaction time, and errors, without inflated claims.
10 questions these guides answer.
Each one opens the guide at the answer.