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Sleep schedule (click to copy)
Frequently Asked Questions
How long is a sleep cycle?
A sleep cycle lasts approximately 90 minutes. Each cycle includes light sleep (N1, N2), deep sleep (N3), and REM sleep. Adults typically complete 4–6 cycles per night. Waking up at the end of a cycle, rather than in the middle, significantly reduces sleep inertia (the groggy feeling).
How many hours of sleep do I need?
Adults (18–64): 7–9 hours (5–6 cycles). Teenagers (14–17): 8–10 hours. Children (6–13): 9–11 hours. Older adults (65+): 7–8 hours. Consistently sleeping fewer than 6 hours increases risk of obesity, cardiovascular disease, and cognitive impairment.
Why do I still feel tired after 8 hours?
You may have woken up during a deep sleep (N3) or REM phase. Sleep quality matters as much as duration. Other factors include sleep apnoea, irregular sleep schedule, blue light exposure before bed, caffeine, alcohol, or underlying health conditions.
What is REM sleep?
Rapid Eye Movement (REM) sleep is the stage where most dreaming occurs. It's essential for memory consolidation, emotional processing, and creativity. REM periods get longer in later cycles — the final cycles of a full night's sleep have the most REM. Cutting sleep short loses disproportionately more REM.