Body Works: Sleep Quiz

Your comforter might be super-snuggly, but that's not the real reason for curling up in bed. A night or two of skipping sleep can cause someone to have trouble concentrating and be irritable, moody and depressed. Three days with no sleep can cause someone to hallucinate; rats who were continually kept awake eventually died..

No one's 100 percent sure why the body must have sleep, but here's a few offerings: Sleep gives our bodies time to heal themselves and replace old cells; it decreases how much energy we need to consume so we don't need to eat so much; and it lets new memories get organized and archived.

Theta and delta brain waves generally signal periods of deep sleep. These two brain wave patterns are slower than alpha and beta (the ones our brains usually generate when we are awake and more active) and the slower the brain waves, the deeper the sleep.

R.E.M. (or rapid eye movement) is the period of sleep when brain waves can speed up to levels matching those when you're awake. This is when most dreaming happens, and R.E.M. is critical for a restful sleep.

Assuming you haven't done a no-no like smoking cigarettes or drinking alcohol or caffeine too late in the evening, you should experience about 20 to 25 percent R.E.M. sleep a night, split up into three to five sessions.

All mammals dream, and some birds even dream a little. Sadly, reptiles like your snoozing snakes and curled-up chameleons probably aren't visiting dreamland.

Turns out dream analysis could be on to something but probably not as much as some people would have you believe. Dreams happen when the brainstem shoots random electrical charges into the brain. Many believe that as these signals are zipping around, the forebrain is attempting to make sense of them. So at times, the forebrain's analysis of dreams might be telling us a bit about ourselves -- sort of like a Rorschach test.

An average person with regular sleeping habits will spend around a third of their lifetime sleeping -- but they'll also be dreaming for about six whole years.

In a study conducted over six years with more than a million participants, it was found that adults who slept six to seven hours a night had the best chance to beat the odds. Those who slept more than eight hours a night were more likely to kick the bucket.

Research by a team at Oxford University found that counting sheep might not be such a hot idea after all. The task of ticking off endless sheep can be so dull that you quickly lose focus and start thinking of other things.