Excerpt:
Throughout history, there have been numerous accounts of segmented sleep, from medical texts, to court records and diaries, and even in African and South American tribes, with a common reference to "first" and "second" sleep.
Anthropologists have found evidence that during preindustrial Europe, bi-modal sleeping was considered the norm. Sleep onset was determined not by a set bedtime, but by whether there were things to do.
Historian A. Roger Ekirch's book
At Day's Close: Night in Times Past describes how households at this time retired a couple of hours after dusk, woke a few hours later for one to two hours, and then had a second sleep until dawn.
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During this waking period, people would relax, ponder their dreams, or have sex. Some would engage in activities like sewing, chopping wood, or reading, relying on the light of
the moon or oil lamps.
there is
growing evidence suggesting naps can have important benefits for memory and learning, increasing our alertness and improving mood states. Some believe sleep disorders, like sleep maintenance insomnia, are rooted in the body's natural preference for split sleep. Therefore, split sleep schedules may be a more natural rhythm for some people.
For more info:
https://www.sciencealert.com/humans-used-to-sleep-in-two-shifts-maybe-we-should-again