Deep sleep generally occurs at the same time each night (that is, it is to some extent anchored by the circadian clock). To get more and better deep sleep, go t

Deep sleep generally occurs at the same time each night (that is, it is to some extent anchored by the circadian clock). To get more and better deep sleep, go to bed at the same time every night. Since deep sleep tends to dominantly occur early in the night (within the first two hours of falling asleep), you’ll basically lose out on it anytime you go to bed abnormally late. (In the Hindu medicine system there is an adage… “an hour of sleep before midnight is worth two hours, after midnight it is worth one hour, after sunrise it is worth zero hours.” I suspect the circadian anchoring of deep sleep is the prime determinant in this heuristic’s truthfulness.)