[A] history professor at Virginia Tech named A. Roger Ekirch, who spent hours investigating the history of the night and began to notice strange references to sleep. A character in the “Canterbury Tales,” for instance, decides to go back to bed after her “firste sleep.” A doctor in England wrote that the time between the “first sleep” and the “second sleep” was the best time for study and reflection. And one 16th-century French physician concluded that laborers were able to conceive more children because they waited until after their “first sleep” to make love. Professor Ekirch soon learned that he wasn’t the only one who was on to the historical existence of alternate sleep cycles. In a fluke of history, Thomas A. Wehr, a psychiatrist then working at the National Institute of Mental Health in Bethesda, Md., was conducting an experiment in which subjects were deprived of artificial light. Without the illumination and distraction from light bulbs, televisions or computers, the subjects slept through the night, at least at first. But, after a while, Dr. Wehr noticed that subjects began to wake up a little after midnight, lie awake for a couple of hours, and then drift back to sleep again, in the same pattern of segmented sleep that Professor Ekirch saw referenced in historical records and early works of literature.NYT: Rethinking Sleep
I can believe that. I needed to catch up on sleep after a long week last Friday -- laid down for a nap at 5pm, got up from midnight to 1am, and then back to bed to 9am :D
But that short amount of time I was up felt really good, then I was naturally tired again.
Sometimes I get on a cycle of late afternoon naps, up for five-seven hours, then get a few hours of short sleep overnight. I don't find that schedule restful and will eventually force myself to stay up late enough to compress my sleep back into an eight hour block. But I wonder if say a 9pm bedtime, then up for an hour or two around midnight, then back to bed for another five to six hours would work out.
I'm not sure it's just the schedules of an industrialized world either -- farmers, without illumination of even candles and lanterns, undoubtedly wouldn't have slept through an entire 12 or 14 hour long winter night, day after day, especially in the season when physical work was at it's wane.