Records from the 17th century and earlier show that Europeans used to sleep in two segments of four hours, separated by an hour or two of being awake:
During this waking period people were quite active. They often got up, went to the toilet or smoked tobacco and some even visited neighbours. Most people stayed in bed, read, wrote and often prayed. Countless prayer manuals from the late 15th Century offered special prayers for the hours in between sleeps. And these hours weren't entirely solitary – people often chatted to bed-fellows or had sex. A doctor's manual from 16th Century France even advised couples that the best time to conceive was not at the end of a long day's labour but "after the first sleep", when "they have more enjoyment" and "do it better".
The interval also proved ideal for deep thinking:
Dorveille, as the French called this time, signaled the mingling of thoughts that wandered "at will" and that combined in new and exciting ways. "If you could choose an hour of wakefulness out of the whole night," observes Nathaniel Hawthorne, "it would be this." Elsewhere is reported that the Bishop of Salisbury would "rise, light, and after burning out his candle, return to bed before day." Some even prepared in advance for their period of watching. Before retiring, Thomas Jefferson would read works of moral philosophy so as to have something "whereon to ruminate in the intervals of sleep."
Many psychologists believe that our physiology is still geared towards segmented sleep, which would explain the high incidence of insomnia today.