Based on 90-minute sleep cycles — wake up refreshed every morning
Sleep occurs in 90-minute cycles. Waking between cycles feels more refreshing than waking mid-cycle. To wake at 6:00 AM feeling refreshed go to sleep at 10:30 PM (3 cycles) 12:00 AM (4 cycles) 1:30 AM (5 cycles) or 3:00 AM (6 cycles). Most adults need 5 to 6 complete cycles — 7.5 to 9 hours — per night.
Sleep cycles last approximately 90 minutes each and consist of four stages: light sleep deep sleep and REM (rapid eye movement) sleep. Waking during deep sleep or REM causes grogginess and fatigue. Timing your alarm to coincide with the end of a cycle — when you are in lightest sleep — makes waking up significantly easier and leaves you feeling more refreshed.
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