Sleep stages

Your Apple Watch's estimate of how many minutes you spent awake and in REM, core and deep sleep each night.

Through the night you loop between REM and non-REM sleep, roughly every 80 to 100 minutes, usually 4 to 6 times. Deep sleep bunches up early in the night and REM gets longer toward morning.

Apple Watch picks a stage for every 30 seconds from its motion sensor. Deep matches the lab stage N3, core covers N1 and N2 (what other trackers often call light sleep) and REM is REM. These are estimates: when Apple checked the watch against lab sleep studies, the most common mix-up was deep sleep labeled as core. Shorter sleeps of 1 to 3 hours, like naps, are saved as just asleep or awake.

A few things shift the mix. Alcohol delays and shortens REM, even at a low dose of about two standard drinks, and more drinks make it worse. Caffeine trims deep sleep. Deep sleep also declines naturally through adulthood, so comparing with your own nights beats comparing with a friend's.

Pajdo shows minutes per stage, but his mood never hangs on them.

This is general wellness information, not medical advice. If a number worries you, or stays away from your usual for a while, talk to a doctor.

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