Exactly how long we're supposed to sleep each night can vary depending on who you talk to, but we all seem to agree on one thing: you want to get one long, uninterrupted sleep. But it wasn't always that way.
Generally speaking, the recommendation is that we should sleep for about eight hours each night. Historically, people seem to have slept for roughly that long, but there's a key difference - they woke up in the middle of it. As Virginia Tech historian Roger Ekirch captures in his book At Day's Close: Night in Times Past, there are over 500 literary references from Homer to Charles Dickens that note the concepts of first and second sleep, in which people would sleep for a few hours and then spend one or two hours awake before going back to sleep.
Crucially, according to Ekirch, none of these references treat first and second sleep as anything out of the ordinary - this just was the way that things used to be, apparently for thousands of years. The BBC has a cool overview of Ekirch's research as well as new followup work by fellow historian Craig Koslofsky. It includes this look at how people spent this time of mid-sleep wakefulness. Oh yes, you better believe there was sex involved:
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".
According to Ekirch and Koslofsky's works, the second sleep started to disappear beginning in the 1600s among the emerging urban upper class of Europe, and in 200 years the practice had all but disappeared. Improvements in street lighting made it possible for people to stay active longer before going to bed, and suddenly the idea of going to bed early just to wake up in a few hours lost its luster.
The question, then, is whether the decision to abandon segmented sleep was actually the right decision for humanity. Certainly, the fact that uninterrupted rest has caught on so completely that we now pretty much think of it as the natural way to sleep suggests it wasn't a bad decision.
At the same time, there are still plenty of people who regularly will wake up in the middle of the night and have trouble falling back to sleep (I've certainly experienced this phenomenon more often than I'd like) to the point that it now has its own name: sleep maintenance insomnia. This condition might actually just be a throwback to the way humans used to sleep - and how some still do, based on some anthropological research on the sleep habits of certain tribes in Nigeria.
If nothing else, it's probably good to know that waking up in the middl of the night shouldn't be seen as something to worry about - you're just reconnecting with how your ancestors used to sleep, 1500s style. And as long as you're not actually sleeping with your ancestors, I can't see anything wrong with that.