How many hours of core sleep do you need

Sleep is divided into two categories: REM and non-REM sleep. You begin the night in non-REM sleep followed by a brief period of REM sleep. The cycle continues throughout the night about every .

Deep sleep occurs in the final stage of non-REM sleep.

Stage 1 of non-REM sleep lasts as you move from being awake to being asleep.

During stage 1:

• your body functions — like heartbeat, respiration, and eye movements — begin to slow
• your muscles relax with only occasional twitches
• your brain waves start to slow down from their wakeful state

Stage 2 accounts for about of the total sleep cycle.

This is the stage of sleep you may fall into throughout the night.

During stage 2:

• your body’s systems continue to slow and relax
• your core temperature drops
• your eye movements stop
• your brain waves are slow, but you have some short bursts of activity

Stages 3 and 4 are when you experience deep sleep.

During these stages:

• your heartbeat and breathing become their slowest as your muscles relax
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