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Typical sleep pattern in young adults.

Typical sleep pattern in young adults.
Typical sleep pattern in young adults.

Rapid eye movement (REM) sleep occurs cyclically throughout the night every 90–120 min. Brief periods of wakefulness (stage W) occur periodically. Sleep time is spent as follows: Stage N1: 2–5% Stage N2: 45–55% Stage N3: 13–23% REM: 20–25%