If you wake up in the middle of the night for an hour or two, don’t assume it’s a bad thing. According to some research that this article points out, humans may have naturally had two separate sleeps historically. Apparently, since the light bulb was introduced we have stayed up later during the night and possibly changed our natural sleep pattern of waking up for an hour or two, between a first and second sleep.
Something puzzled [Roger] Ekirch as he leafed through parchments ranging from property records to primers on how to spot a ghost. He kept noticing strange references to sleep. In the Canterbury Tales, for instance, one of the characters in ‘The Squire’s Tale’ wakes up in the early morning following her ‘first sleep’ and then goes back to bed. A fifteenth-century medical book, meanwhile, advised readers to spend the ‘first sleep’ on the right side and after that to lie on their left. And a scholar in England wrote that the time between the ‘first sleep” and the ‘second sleep’ was the best time for serious study.
Numerous other studies have shown that splitting sleep into two roughly equal halves is something that our bodies will do if we give them a chance. In places of the world where there isn’t artificial light — and all the things that go with it, like computers, movies, and bad reality TV shows — people still sleep this way.
We Used to Sleep Twice Each Night (Delancey Place)