I've read other things that indicate that the "average human sleep cycle" is actually one and a half hours. I've also read that a person who wakes up (or is waken up) in the middle of one of these cycles is likely to feel worse than if they woke up at one of the ends of the cycle.
What that means to me is that if I know I'll be a little short on sleep, but have only 5 1/4 hours until I have to get up again, I'll probably feel better if I stay awake 45 minutes longer rather than going to sleep right now. (That will give me 4 1/2 hours, or 3 complete cycles, of sleep.)
...I know, I know; a little "off topic" for the perlmonks...<?p>