"Many of us are still very perplexed about the functional role of sleep," says Dr. David Kupfer, who studies sleep at the University of Pittsburgh. But sleep researchers do know a few tricks for keeping awake. Among them:

*Try to avoid staying awake by yourself. Talking to other people helps keep alertness higher.

*Play music and sing along.

*Move around as much as possible.

*If you're driving, open the car windows and let the wind blow on your face for extra stimulation.

*Blasts of cold air and splashing your face with cold water will also increase alertness.

*Eat, but avoid high-carbohydrate foods, such as crackers, pasta, cereal, cookies, cake and candy, which can increase sleepiness by raising brain levels of serotonin -- a naturally calming neurochemical. Instead, aim for high-protein foods.

*If you know ahead of time that you have to stay awake for an extended period, prepare yourself. Sleep experts recommend sleeping as much beforehand as possible.

*For unanticipated sleep loss, try not to stay up all night. Instead, gain extra waking time by shortening your normal sleep cycle. Go to bed an hour or two later and get up a hour earlier. This technique seems to increase alertness, despite some sleep deprivation.

If you must stay up for a couple of days straight, be sure to take a nap -- and do it early, preferably on the first day of missed sleep. Two hours of napping can buy another 24 hours of pretty good alertness, says the University of Pennsylvania's David Dinges.

But if you wait until the second day of no sleep before taking a nap, you will probably wake up feeling worse and much less alert than when you went to sleep.

"The longer you wait, the greater the sleep debt," Dinges says. "It's like losing money at a poker table. There's just no possible way that you can cover the IOUs by the end of the game."