Lately I find that my sleep is segmented; I was wondering if it's a bad thing. I generally sleep from 3am to 8am or so, and then I wake up, eat an apple, and read the Internet. And then I sleep from 9am to 11am again. It's been pretty consistent for awhile. It seems to be the pattern of 2 REM cycles and then 1, since I believe people generally get 3 in a night.
It's perhaps not the same thing, since it seems unrelated to daylight. It may be related to information retention. I generally wake up and write some notes about what I thought about during my sleep (lately I find that my dreams are almost like thinking). And then I do some googling related to those topics. And then I go back to sleep and retain it.
Another thing that's interesting about sleep is that humans have a dimorphism between early birds and night owls. I read a hypothesis that it's because it maintains the property that some members of a group are a awake at all times, e.g. to guard against predators and so forth.