This article, The myth of the eight-hour sleep, suggests that some sleep problems relate to our not having really adapted to having a long sleep at night. It says that before artificial lighting was prevalent people slept in two stages with a gap in between in which they did things, prayer, sex, reading, socialising . . . (This would seem to me to be easier for people of means who could afford candles. And naps aren't mentioned.)

Mona Evans
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