Sleep latency
Minutes you typically take to fall asleep
min
Cycle length
Adults average 90 min; range 80-110
min
Circadian sync
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The Golden Window: 22:00 - 02:00
Slow-wave (deep) sleep is governed by adenosine pressure and a melatonin-aligned drop in core body temperature.
Both peak in this 4-hour band. Sleep that begins here typically delivers the deepest recovery, hormone release and immune consolidation --
even if total duration matches a later bedtime. Late starts compress deep-sleep capacity regardless of total hours.
90-Minute Sleep Cycles
A full sleep cycle moves through N1 → N2 → N3 (deep) → REM, averaging ~90 minutes for adults (range 80-110).
Waking between cycles avoids interrupting deep or REM stages, drastically reducing sleep inertia (the groggy, slow feeling on waking).
Deep Sleep (N3)
Concentrated in the first half of the night. Drives tissue repair, muscle growth, immune memory and glymphatic brain clearance.
REM Sleep
Heaviest in the second half of the night. Critical for memory consolidation, skill learning, emotional regulation and creativity.
Sleep Latency
Healthy latency is 10-20 minutes. Under 5 = likely sleep-deprived. Over 30 = check stress, caffeine after noon or screen exposure.
Light is the Anchor
10 minutes of bright morning light locks the circadian phase. Dim warm light after sunset preserves the natural melatonin rise.
Sleep Debt & Consistency
The body weights bedtime regularity more than total hours. Going to bed within a 30-minute window each night
produces measurably better cognitive performance than the same hours of irregular sleep. One full night of recovery does not erase a week of debt.
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