Hey! I am in college and I go through the same stuff. Sometimes, if I have had 6 or more hours of sleep the night before, i'll go and get on the elliptical and it actually gives me energy. ^_^ so, you decide, if you are totally beat, sleep. Sleep is always nourishing and it helps so tht you don't experience moodiness. However, 8 hours of sleep and you have free time: hit the gym. Make schedules too to fit it in, that helps me a ton. I'm no doctor but...Hope that helped

If you're really sleep deprived, definately take a nap. I'd suggest exercise also though, so to try to fit them both in, try taking a pretty short nap, around maybe 20 minutes. You'll feel more refreshed because your body hasn't gotten into a deep sleep mode yet, and you'll also have time to work out which will make you feel even better.