I've had trouble sleeping since college. Initially that took the form of insomnia, but more recently I've fallen into a more disruptive, two-part sleep pattern. When this happens I sleep for four hours, get up for an hour or two, then go back to sleep for another two or three (or, if I'm really unlucky, I stay up the rest of the night).
As an adult I've attributed this to stress and anxiety which give me a thousand things to worry about at 2 a.m. as well as a certain genetic predisposition toward insomnia. It's a trait I share with my mom, and I've seen showing up in my daughter as well.
It turns out we just might be throwbacks to an earlier kind of sleep pattern. Our ancestors had the concept of a "second sleep", the idea being that you went to bed when night fell, slept for a few hours, woke up for an hour or two, and then went back to bed for the rest of the night.
There are a few posts that talks about this:
- SlumberWise: "Your Ancestors Didn’t Sleep Like You"
- Fortune.com: Why you can't sleep
- BBC: The myth of the eight-hour sleep
The consensus is that steadily increasing street lighting in cities made it safe to work and play at night. We started staying up later and going to bed later. Over time our sleep patterns changed to accomodiate the 8 hour block that so many of us strive for (and many fail to achieve).
I blame the kids for my two-part sleep pattern. In the old days I might have stayed up for a day or two with short term insomnia. It'd reset my internal clock and I'd sleep blissfully for a few weeks or months. With kids though, that trick didn't work. If I did stay up for 24 hours, I'd crash into sleep the next day only to be woken two hours later by a sick, crying baby. Once the kids started sleeping through the night, I still slept lightly. I found myself settling into the second sleep pattern for weeks on end.
If you think about it, the idea of a second sleep makes. Sleeping in an uninterrupted eight-hour block seems like an excellent way to get eaten by a stealthy sabertooth tiger. Maybe it's just too many midnight attacks during Dungeons & Dragons scenarios, but having multiple people sleeping through the night in staggered 4 hour blocks seems a lot safer.
I find the whole idea fascinating. Here's this quirk of human biology, forgotten for a century but unearthed through a combination of modern sleep studies and the study of historical literature. It'd also be nice to know that weird sleep habits might not be that weird after all.