This is one of those little quirky things that caught my eye about sleeping.
It turns out that eight hours straight sleep is not normal.
Up until the industrial age, people would have two sleeps every night.
They’d go to bed early and sleep for about four hours, then get up for an hour or two, then back to sleep until morning.
Very handy for astronomy.
Cheers,
Renato
http://www.history.vt.edu/Ekirch/sleepcommentary.html