There was a mild flurry about a year ago around the release of Evening’s Empire, by Craig Koslofsky. Like the 2005 book by Roger Ekirch, At Day’s Close: Night in Times Past, Koslofsky’s book examines pre-electric lighting patterns of behaviour at night, including sleep patterns. The BBC has a nice article on the two here. Both Koslofsky and Ekirch assert that until the 19th century, humans typically slept in two blocks of about 4 hours each, and scientists confirm this natural tendency.
Last year, between December and March, I had the luck to test this theory, and once again, it seems I will be sleeping old school, in blocks of time. Unfortunately, these blocks of time are often 2 hours and not 4 hours, as the scientists and historians claim we need. User testing of one shows me that 2 hour sleep blocks (or 4 hours followed by 2 hours) are inadequate and I may be near-hallucinatory by March, just as I was last year.
When doing living history, its always better not to skimp on resources.
Kitty Calash 
I’ve always wanted to try the whole “second sleep” thing – I should have during my December break, when I didn’t have to go to work! But I do have a horror of not being able to fall back asleep after that middle period.
Oh, that not falling back asleep is the killer. Or falling asleep too late! It would have to be a vacation experiment, because missing school or work is too panic-inducing. Two sleep cycles work really well if you can sleep in until 8 or so; I got a lot of reading done that way this weekend. Of course, I haven’t tested my recollection of that reading yet…!