Earlier this summer, Mike Trevino, 29, slept nine hours in nine days in his quest to win a 3,000-mile, cross-country bike race. For the first 38 hours and 646 miles, he skipped sleep entirely. Later he napped--with no dreams he can remember--for no more than 90 minutes a night. Soon he began to imagine that his support crew was part of a bomb plot. "It was almost like riding in a movie. I thought it was a complex dream, even though I was conscious," says Trevino, who finished second.

Trevino's case may be extreme, but it raises important questions: If we don't sleep (or sleep enough), what happens to our dreams? And if we don't dream, what happens to us? These are not purely academic or existential questions. Nearly 40 percent of Americans report getting fewer than seven hours sleep on weekdays and nearly 60 percent say they experience some kind of insomnia at least several nights a week, according to a National Sleep Foundation poll. "Sleep may be essential for life," says Jerry Siegel, a neuroscientist at UCLA's Center for Sleep Research. "It's certainly essential for optimum brain function."

For those of us who are stressed, anxious and working too hard, insomnia only makes things worse. When our worries wake us in the middle of a REM cycle, issues that might have been resolved through dreams are left hanging. Dreams tend to get more positive as the night wears on, and waking up too soon interrupts this process. "People who are sleep deprived are often irritable," says Rosalind Cartwright, chairman of psychology at Rush University Medical Center in Chicago. "They haven't worked through the bad feelings."

Clinical depression interferes with healthy sleeping--and dreaming. In a study published this month, Eric Nofzinger and his colleagues at the University of Pittsburgh found that depressed dreamers crank up their limbic systems more than other dreamers. "The brain of depressed dreamers doesn't shut off," he says. "It keeps ruminating about things, which makes it hard for the person to get to sleep--or if they do, it wakes them up in the middle of the night to work on all the problems they have."

Rats eventually die when they don't get any REM sleep. Humans don't. Yet the drive to dream is relentless. Some studies have shown that when humans are deprived of REM, they begin to have vivid, REM-like dreams during their non-REM phases. After days of not sleeping, people begin to do something like dreaming while awake, as Trevino's experience shows, says Cartwright.

You can't bank sleep or REM either--although the body seems eager to try. When people who are sleep deprived finally do hit the pillow, they have what scientists call "rebound REM": extra-long REM cycles, which can lead to hypervivid dreams and even nightmares, says UCLA's Siegel. "The REM sleep during the rebound is more intense psychologically."

If you know you have trouble sleeping, here's what to do: Find out if you have a physical problem such as sleep apnea (which interrupts breathing during sleep). If you're physically fine, go to bed and get up at a regular time every day, stay away from caffeine and alcohol before bedtime, develop sleep rituals and avoid bright lights in the bedroom. Good sleep produces good dreams. "You'll work better, feel sharper, actually be more creative," says Cartwright. No wonder they say that dreams are sweet.