If you find yourself stressing about getting eight glorious hours of sleep — and then finding yourself unable to sleep, well, because you should be sleeping instead of worrying — then this research might peak your interest. When isolated from sunlight, humans follow a very predictable sleep pattern: In the absence of light, people will sleep for four hours, wake up for a few hours, and then go back to sleep for four hours more.

References to this “second sleep” have appeared throughout human history according to the research of Virginia Tech history professor, A. Roger Ekirch. Old diaries, medical journals and legal depositions have documented the phenomenon of “biphasic sleep” for centuries. Could this be the “right” way to sleep? Check out the video above to find out why we’re no longer following the sleep habits of our ancestors. Then let us know in the comments how much sleep you need to feel rested.