• You can make up a sleep deficit, but it takes time. There's no way to catch up when you're sleep deprived for years. Research indicates those people shave years from their lives, says Dr. Tom Cloward of LDS Hospital's sleep center.

• Sleep disorders are linked to diabetes, stroke, heart attack, obesity and other serious medical problems. It's not always clear, though, which triggered the other.

Sleep is a chance for the brain to recharge, much like a car battery needs to recharge, although the brain itself does not sleep. Restful sleep occurs in cycles that last about 90 minutes and include REM (rapid eye movement) sleep, followed by four stages of ever-deepening non-REM sleep.

It's a myth that older people need less sleep. Barring health problems that interfere, sleep patterns should continue as they did when someone is younger.

How do you know if you're getting enough — or getting good sleep?

The most common symptoms of sleep problems include trouble falling asleep, waking often at night, waking too early and not going back to sleep, waking up unrefreshed, snoring, pauses in breathing, shallow breathing or an unpleasant feeling in the legs. When they begin to disrupt waking hours, it's time to seek help.

Often, it's hard to convince people their poor-quality sleep is affecting them. "They think they function just fine. But in alertness or concentration tests, they usually score below normal," says Dr. Gregory P. Dupont, a pulmonologist and sleep specialist at Salt Lake Regional Medical Center.

Dr. Kevin Shilling, sleep specialist at LDS Hospital, cites a study that compared alcohol intake to a night without sleep. The tired participants had reaction times very similar to those of someone who drank eight beers. "They made the same mistakes" as someone who was legally drunk, he says.

The National Highway Traffic Safety Administration estimates as many as 100,000 police-reported crashes are caused primarily by sleepy drivers, most of them in early to mid-afternoon and in the very early morning.

A stunning 60 percent of American adults in the 2005 Sleep in America poll said that in the past year they've driven a motor vehicle while drowsy; 37 percent say they have at some point in their lives fallen asleep or nodded off while driving.