"Don Quixote followed nature, and being satisfied with his first sleep, did not solicit more. As for Sancho, he never wanted a second, for the first lasted him from night to morning."  - Miguel Cervantes, Don Quixote (1615)

Do you get out of bed in the middle of the night? It turns out you might be more in tune with your natural rhythms then you think.  Second sleep, also called segmented sleep, or bimodal sleep, is a biphasic sleep pattern that views middle of the night waking as a productive time to talk with bed fellows, pursue creative endeavors, or meditate. This window is approximately one hour, and research shows that the pituitary gland produces high levels of the hormone prolactin during this time. Prolactin is believed to contribute to an overall sense of relaxation that many people experience during this night waking.  The state is similar to hypnagogia, the feeling of waking from slumber, and hypnopompia, the feeling experienced when coming out of sleep. 

Historian Roger Ekirch of Virginia Tech, and author of  "At Day's Close: Night in Times Past," spent sixteen years studying the evidence of second sleep. He found over 500 references to this type of sleep in diaries, court records, anthropological journals and famous works of literature. He hypothesizes that the Industrial Revolution along with the invention of electricity, street lamps, and coffeehouses contributed to a decline in the practice of segmented sleep as people increased productivity and decreased rest during night hours.  Ekirch credits many of today's sleep issues to the body being forced out of it's natural circadian rhythm. The use of artificial light, such as omitted from television and electronic devices, may further contribute to the well known phenomena of sleep maintenance insomnia, or inability to get back to sleep after waking up in the middle of the night.

Despite the research by Ekirch and other historians, popular culture still maintains that we need eight hours of uninterrupted sleep despite the substantial evidence that this kind of slumber may actually be our evolutionary circadian rhythm. In the 1990s psychiatrist Thomas Wehr conducted a study that placed people into complete darkness for 14hrs each day for a month. Within a short time the subjects naturally adjusted their internal clocks to follow a distinct pattern of four hours of sleep, one to two hours of wakefulness, and another four hours of sleep.  Other researchers back up the idea of bimodal sleep including  Dr Jacobs, insomnia specialist of the U Mass Memorial Medical Center and author of  "Say Goodnight to Insomnia."  In an interview with Huffington Post, Jacobs states that, "polyphasic sleep pattern lies dormant in our physiology, met an evolutionary need, and therefore may be adaptive rather than a sleep disorder."  

Russell Foster, professor of circadian neuroscience at Oxford seconds this idea, and encourages people to stop panicking if they wake up in the middle of the night. In an interview on RN, Australia's Broadcasting Network, Foster says, "many people of course wake up in the middle of the night and they think, oh my goodness, that's it, I'm never going to get back to sleep, I might as well just abandon sleep now, go down and have a cup of coffee and start work, or whatever. And in fact what they should be doing is saying, okay, well, chances are if I just stay relaxed, keep the lights relatively low, do something relaxing, maybe listen to a piece of relaxing music or read a little bit of a book, then the chances are I can probably get back to sleep again. It doesn't happen for everybody and that's because there is genuine insomnia. But for many people who wake up in the middle of the night it could be a throwback to that earlier biphasic pattern of sleep. The critical thing is to stay calm, stay relaxed, and not do things that will increase alertness and therefore reduce your chance of getting back to sleep again for that second phase."

So the next time you wake up in the middle of the night, take a deep breath, get up, and try handwriting out some ideas for that novel you've been meaning to write. It might be exactly what your body needs.