Sleep is done in 4 stages: Stage 1 (transitions from awake to sleeping in 10 minutes), Stage 2 (body temp drops and heart rate slows. last around 20 mins), Stage 3 (dropped breathing rates and BP, muscles relax. Deepest sleep), Stage 4 (Rapid Eye Movements occur, brain becomes more active, body is immobilized).
Personal note: Sleeping is like a game: Each stage is like a level and you need to complete the previous one to get the next rewward. Sleeping for one long period is better than scattered sleep throughout the day. Benefits of napping only affect some people.
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