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Learn how sleep stages and sleep cycles change through the night, including 70-100 minute first cycles and longer REM periods.

Learn how long each sleep stage lasts, from light sleep to REM. See how normal sleep cycles change through the night and what it means.

Compare light sleep vs deep sleep vs REM sleep, how each stage works, and why light sleep takes nearly half of a normal night.

Learn what happens during REM sleep, from increased brain activity to muscle relaxation, shifting breathing, and vivid dreaming in this sleep stage.

Learn how many sleep cycles per night most people get, what affects them, and how sleep duration changes the number of cycles you complete.

Learn how much sleep adults need, with CDC guidance showing most adults need at least 7 hours and why the 8-hour rule is not exact.

Learn what happens during deep sleep, including N3 brain activity, physical recovery, and why this stage matters for restful sleep.

Learn how to track sleep stages at home using wearables, what the data can and cannot show, and how to read sleep stage trends.