True that there's variation among people, but the averages are off. According to the Brigham guys who conducted the recent studies on resident fatigue-related medical errors/car accidents, the average amount of sleep needed by an individual is 8.4 hours per 24 hour period (with individual variation being really wide, between 4-12+ hours), which requires about 9 hours of actual in-bed time to account for the time it takes to fall asleep, physiologic awakenings during sleep, etc. Chances are that you're sleep deprived, like most of the rest of the population (and esp med students), so whenever you do something that isn't all that exciting (like reading med books), your brain falls asleep because it's trying to make up your cumulative sleep debt. You probably need to sleep more. Time of day matters too, because your individual circadian rhythm will make you more or less awake at different times. If you're really a night person it sucks because studying in the middle of the night doesn't really work well with a typical med school schedule. I agree with others, try caffeine, exercising, whatever works. If it gets really bad (esp during years 3/4) you might want to talk to a sleep doctor.
