There's a thing called Delayed Sleep Phase Sndrome. It's a circadian rhythm disorder that affects maybe 1/2 of 1% of people (but seems to be more prevalent among engineers and software people, possibly because DSPS sufferers choose vocations that allow for flexible schedules). Essentially, DSPS people have a natural sleep-wake cycle that's shifted a few hours from the norm. My natural cycle is to sleep at about 2:30am and wake at 11:30. I can force myself into a "normal" schedule, but I can't change my natural circadian rhythm, so I suffer from various effects of sleep disruption that are similar to jetlag. For some reason, a high proportion of teenagers, particularly boys, experience temporary DSPS during their adolescence. It can be as many as 20%. I suspect that the natural creeping of the circadian rhythm that happens during adolescence (as mentioned in this article) kicks into overdrive for some kids, and gives them DSPS-like symptoms during that time. Most of these kids grow out of it and re-establish a normal rhythm into adulthood. People like me, however, keep their DSPS throughout their lives. (And it's hereditary. I got it from my mother) http://en.wikipedia.org/wiki/Delayed_sleep_phase_syndrome