In 2001, 38 percent of U.S. adults said they were less than they were just five years earlier. Americans now average seven hours in bed per night, and close to 60 percent now report they have trouble sleeping at least a few nights every week.

Seduced by 24-hour casinos, Seinfeld reruns and the Internet, Americans have plenty of diversions to keep them wired and alert. Did we mention L.L. Bean, the store that never closes? There's always good old worry, the anguish of relationships gone wrong and, right up there with the best of the sleep-wreckers, the dour discomfort of gastroesophageal reflux.

The biggest sleep robber of all, however, is work—the puritan ethic gone haywire in an era of global markets. To accommodate the relentless pressure for , we're sleeping less and spending less time in social and leisure pursuits; the resulting can steal away even more sleep. Consider this: We're not only missing more shut-eye, we're having less , too.

To some degree, we can sacrifice sleep to oblige other demands on our time, but we pay a high price for the privilege. The need for sleep, anchored in part to the most ancient rhythms of the planet, is etched deeply in our brains. When we interrupt the natural rhythm of day and night for any reason—even reveling—we risk setting off a cascade of problems.

What we do at night affects everything we do during the day—our ability to learn, our skills, our memory, stamina, health and safety. Most of all, it affects our mood: Chronic sleep disruption appears to be the single biggest trigger for .

Everyone has a troubled night sometimes, or even a run of them, which happens to the average person about once a year. It's part of being human, subject to stress and worry. But it's what we do in response to it, experts say, that determines whether we will wind up with chronic insomnia. It turns out that the best thing to do in response to a bout of is often, well... nothing at all.

Two Systems, One Sleep

Recently, scientists have come to recognize that sleep is regulated by two entirely different systems. The knowledge that we have two roughly parallel forces guiding our need for sleep has opened the bedroom door to multiple ways of treating insomnia.

One force is the sleep homeostat. This functions like a drive that "builds up during wakefulness in pretty much a linear fashion and is discharged when you sleep," explains Arthur J. Spielman, associate director of the Center for Sleep Medicine at New York Presbyterian-Cornell Medical College. The homeostatic pressure to sleep depends not only on how long you are awake but on how active you are while awake.

But if you build up a need for sleep in a linear fashion, one would think you'd get sleepier as the day proceeds. It doesn't happen quite that way. Enter , the body's biological clock. The circadian system is tied, albeit imperfectly, to cycles of light and dark. We have dedicated sensors on the retina that deliver the daytime/nighttime message directly to the pineal gland tucked deep inside the brain. In response to darkness, this tiny nodule of brain tissue produces the sleep-inducing melatonin, broadcasting the sandman's message to brain areas that govern everything from body temperature to protein synthesis to hormone production to alertness.

Circadian rhythm guides the body through cycles of sleep and alertness. Ironically, it issues its strongest alerting force in a burst lasting from 6 p.m. to 8 p.m., perfect for dinner-party repartee (although you may not remember the bon mots— is sharpest around 7 in the morning). After 8 p.m., alertness begins to fade, permitting us to doze off. This same system makes us sleepiest in the early morning, from 4 a.m. to 6 a.m. Stay up all night studying for an exam and circadian forces will make you drowsy near dawn. Stick it out for two more hours, though, and you'll start picking up steam again. "You don't need sleep to actually get alert," Spielman points out.

Understanding this cycle can help some people who have trouble falling asleep or getting back to sleep. Manipulating the circadian rhythm with bright lights in the morning or melatonin in the evening, says Spielman, can help.

By the same token, it's possible to ramp up the sleep drive by tinkering with the sleep homeostat. Two of the best methods are exercise and heating the body. Grandma was right about that warm bath before bedtime, although she may not have known why. As it turns out, sleep naturally follows a sharp drop in body temperature. So still in bed after a hot bath may be just what your body needs to drift off.

Many of us complain that we struggle to get enough sleep. But insomnia is one of those words we toss around a bit too freely. Experts generally apply the "30-30 rule": It's insomnia if it takes you 30 minutes or more to fall asleep or if you're awake for 30 or more minutes during the night—at least three times a week. No matter how little you sleep, it isn't insomnia unless your nighttime habits drag you down during the day.

Those who have trouble falling asleep or waking up may not technically have insomnia but instead be suffering from "sleep-phase disorder." In this case, people have unwittingly trained themselves to conk out at the wrong time. It's especially common among adolescents and college students—those who yield to all the siren calls for their time, don't get to sleep before 3 a.m. or 4 a.m. and then can't get up for classes. (If you have insomnia four or five nights a week but not on weekends, you probably have a phase-shift problem.)

Sleep patterns also shift during life. Believe it or not, "You don't want to sleep like a baby," says Michael L. Perlis, associate professor of psychiatry and psychology at New York's University of Rochester and director of the behavioral sleep medicine service there. "You want to sleep like an adolescent." Babies wake often; they are not yet able to consolidate sleep into one stretch. Adolescents sleep like there's no tomorrow.

For most people, it's downhill from there. means accommodating the sleep habits of another person, a biological minefield if a late-to-bed "owl" falls in love with an early-rising "lark" and tries to go to bed a couple of hours earlier than his body prefers. Childbirth brings, well, children, and women typically learn to be vigilant during sleep and never unlearn it; they become so fine-tuned to noise that the habit of waking easily stays with them the rest of their life. "Child rearing is the number-one precipitant of insomnia," says Perlis.

Insomnia typically starts innocently enough. Something gives you one bad night—or a few. You twist your knee and the pain torments you all night. You're jet-lagged. You your spouse is having an affair. Heartsick or , you just can't fall back asleep.

The worst is yet to come. After one bad night, most people experience a great deal of frustration and anxiety about falling asleep and staying asleep. So you try to compensate. You nap in the afternoon or go to bed early. Or you sleep late the next morning, or you have a couple of drinks before bed. That only makes matters worse. You go to bed and, without the accumulated need for sleep, you stare at the ceiling half the night. Or—especially if you've had a few cocktails—you're wide awake at 4 a.m. Now you're even more tired and worried about the consequences of not sleeping than you were the day before—while you're at your greatest vulnerability to irrational thought. Is this, you worry, the beginning of decrepitude?

Pretty soon, this self-defeating cycle takes on a life of its own. Under the influence of anxiety, your brain learns very quickly, without your knowledge or consent, to associate the bedroom with wakefulness. You lie down to rest and your brain goes on high alert. "It has been shown that people who have difficulty falling asleep are supersensitive to bedroom-related stimuli," explains Perlis. "They become physiologically aroused in the bedroom environment"—their switches on just when they want it to calm down.

It's the psychophysiologic equivalent of the perfect storm, the sudden collision of mind, body and environment. The actual experience, though, is more demoralizing than dramatic: You fall asleep in front of the television. You get up out of the armchair at 1:30 a.m. and stumble into bed. Suddenly you're wide awake. There are now a million things to think about, including how much you need sleep to be at your productive best for tomorrow. Says Perlis, "Rumination and worry—cognitive elements—put gas on the fire."

No matter what sets off the sleeplessness in the first place, faced with bedtime, your brain kicks and screams like a 3-year-old. "The mind can get set in the default mode of wakefulness," says Spielman. "It gets stuck in the scared, dangerous, vigilant zone."

There's another variety of insomnia that results not from lack of sleep but from a misperception: Your brain thinks you are awake when you are asleep. Normally, during slumber the brain's information and sensory-processing equipment go offline. The unconsciousness of sleep also "bleeds" slightly into wakefulness, so that most of us can't remember falling asleep, and we are not fully alert when we wake up. That's why we don't remember waking up in the middle of the night—despite the fact that all of us normally wake up 5 to 10 times each night.

In some people, though, one part of the brain stays online while the rest is offline. Consciousness intrudes on sleep, and these people drag themselves out of bed in the morning, swearing, "It takes me a couple of hours to fall asleep," and "I'm awake most of the night." When they are hooked up to sleep monitors, though, they seem to be sleeping just fine.

Sleeping Off the Enemy

Where insomnia is concerned, we're our own worst enemies. No matter how sleeplessness starts, it easily gets locked in place by our own behavior. All of the tactics people usually resort to in order to feel better after a bad night—napping, sleeping in, going to bed early—tend to undermine the body's natural inclination to right itself after a short bout of insomnia.

As a result, the most powerful attack on the monster of insomnia is to do nothing at all. The first and best approach to sleeplessness is to let the sleep homeostat right itself, without making any attempt to compensate. It's also possible that the prompt use of a sleeping pill—say after a couple of sleepless nights, rather than after several wretched months—can get the natural mechanism back on track.

That's welcome news, given what's known about the destructive power of persistent insomnia. Chronic insomnia brings on irritability, headaches and muscle pain. It destroys and mental well-being, it weakens coping skills and robs vitality. It undermines intimate relationships. On-the-job injury rates soar 400 percent for the sleep-deprived. Sixteen percent of absenteeism is associated with insomnia, adding up to $50 billion a year. "Presenteeism"—inability to focus on the job while there—brings the total cost to $150 billion. "Insomnia is the bastard cousin to everything," says Perlis.

It also seems to be the true mother of depression. Most depressed people have trouble sleeping. But insomnia is not just a symptom: It's the single best predictor of depression, says Perlis. He has found that two or more weeks of sleeplessness increase the risk of a first episode of depression by 400 percent—even for someone who has never before been depressed. For those who have struggled with depression before, insomnia often heralds a recurrence.

Perlis contends that insomnia is actually "an unleashing factor" for depression. His longitudinal studies show that insomnia often precedes episodes of depression by about five weeks.

In depression, the architecture of sleep goes awry. Normally, during the course of the night, we gradually slip into deeper and deeper slumber. After hitting the deepest stage, we burst into dream sleep, marked by dramatic brain activity and ( ). Normally, we cycle through these stages of sleep every 90 minutes or so.

But the depressed are on a fast track to dreamland. They dive too quickly into REM sleep, which lasts nearly twice as long as it does in the nondepressed. It's also a souped up version of the REM phase. It's more intense—parts of the brain that deal with emotions are more activated and the depressed sleeper tends to fidget much more.

It seems that at least one purpose of REM sleep is to promote the consolidation of memory, to reinforce what we learn during the day and integrate it into long-term memory—and to strip new memories of whatever emotional charge they initially carried. "You especially need REM sleep when you're depressed to process negative affect," explains Michael Thase, professor of psychiatry at the University of Pittsburgh Medical Center and Western Institute and Clinic.

But in the depressed, "there's so much water in the dam, it can't be contained," says Perlis. The central nervous system stays aroused. Mental hyperactivity, particularly intense in the amygdala and limbic cortex of the "emotional brain," leads to an increase in negative thoughts. The depressed become overly biased to remember bad things. And instead of helping to regulate mood, REM sleep in the depressed actually worsens it. The memory is "always as bad as it was the first time," says Perlis. One common problem in depression is awakening in the early morning. This may be the body's attempt to reduce negative affect by interrupting the last (and normally the longest) cycle of REM sleep.

Most intriguing, the evidence suggests that treating insomnia may forestall a first episode of depression, or a recurrence, and at least keep insomnia from becoming chronic. "It may be," says Perlis, "that if we get rid of the insomnia, we get rid of the depression risk." And that is one more reason not to panic the next time you find yourself wide awake at 3 a.m.