A night of sleep is not one flat block but a chain of roughly 90-minute cycles, with deep N3 crowded into the first half and REM stretching longer toward morning. The brain waves change with every stage, from waking beta down through theta to delta at 0.5 to 4 Hz in the deepest stretch. Sleep deprivation piles up a debt the body repays by plunging straight into N3; jet lag throws the SCN clock, melatonin and cortisol out of phase with local time.
A night of sleep is not one flat block but a chain of roughly 90-minute cycles, with deep N3 crowded into the first half and REM stretching longer toward morning. The brain waves change with every stage, from waking beta down through theta to delta at 0.5 to 4 Hz in the deepest stretch. Sleep deprivation piles up a debt the body repays by plunging straight into N3; jet lag throws the SCN clock, melatonin and cortisol out of phase with local time.
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