Z-z-z-z-z.

Every body has to have it. And suddenly Americans seem desperate to get it.

The search for deep, uninterrupted, refreshing sleep, has become a national obsession. It's driving everything from the development of new prescription sleeping pills to extensive bed makeovers in hotel chains.

In just 10 years, certified sleep clinics in the U.S. have nearly tripled — from 297 in 1995 to 883 so far this year, with more on the way. Sleep medicine has recently become an approved specialty and the number of sleep doctors is soaring — doubling in the past decade to 3,000 today.

Sleep medicine ads are unavoidable (unless you are asleep). In 2004, the makers of top-selling prescription sleep aids spent $61 million marketing their insomnia pills, according to the media research firm TNS Media. In the first seven months of this year, they spent $120 million. The biggest outlay came from Sepracor Inc., buying $57 million worth of TV ads in hopes of winning blockbuster status for its new Lunesta — the first prescription sleep aid that doesn't advise only short-term use. Who hasn't seen that softly glowing Lunesta lunar moth?

Sleep experts say they've never before seen so much interest in sleep.

There has always been fascination with this mysterious part of the daily human cycle, says Karl Doghramji, head of the sleep disorders clinic at Thomas Jefferson University Hospital in Philadelphia. "Everyone sleeps; it's a common experience — you basically fall asleep, and seven hours later, wake up. There's a natural curiosity about that period of time."

But what is new is broadening medical knowledge about sleep patterns, sleep disorders and the severe consequences of too little sleep.

Research has grown from the discovery of REM (rapid-eye-movement) sleep in 1957 to a more sophisticated understanding of sleep phases and the brain cells that regulate them. In the 1980s, experiments with rats proved that weeks of total sleep deprivation led to death. Now we know that mere sleepiness is deadly, too: An estimated 100,000 auto accidents a year are caused by drivers asleep or drowsy at the wheel.

"Sleep is just as important as exercise or what we eat to our overall health," says Carl Hunt, head of the National Center on Sleep Disorders Research.

The public has followed sleep discoveries avidly.

"One generation ago, the word apnea was not even in the vocabulary of the average person," says Meir Kryger, a sleep specialist on the National Sleep Foundation board. "Now everyone uses the word apnea like they learned it in grade 5."

While there's no clear evidence that sleep disorders are growing, the numbers are high enough to support a robust sleep industry. An estimated 10 percent of American adults suffer from chronic insomnia and 5 percent to 7 percent have sleep apnea.

Population changes could push those numbers even higher. Apnea — the repeated cessation of breathing during sleep — is often related to obesity, and obesity figures are rising. Insomnia worsens with age and the onset of menopause, and hordes of baby boomers are entering the danger zone.

Don Delson, a 54-year-old investment banker, wryly observes that younger people sleep more soundly because "in your 30s, you aren't mature enough to worry whether your kids will find the right mate; your bladder doesn't get you up."

His own fix for a sound sleep? For himself and his family, Delson has purchased four Duxiana beds (average price $4,500 each). Swedish-made DUXs, which offer "advanced technology in sleeping" for up to $9,000 a bed, are at the higher end of a growing super-bed industry promising Americans better trips to the land of nod.

Pills, though, are increasingly the sleep aid of choice.

Americans spent $2.1 billion on the top prescription sleeping pills in 2004, according to the pharmaceutical information company IMS Health.

And a recent survey by the mail and retail prescription drug supplier Medco Health Solutions Inc. found remarkable increases in sleep drug use: From 2000 to 2004, the number of adults using sleep medications doubled. In children ages 10 to 19, sleeping-pill use rose 85 percent.

The top sleeping-pill seller by far is Sanofi-Aventis' Ambien ($1.8 billion in sales in 2004), but Sepracor's Lunesta, introduced earlier this year, hit second place with sales of $112 million between January and July, said IMS. Nipping on Lunesta's heels are the new extended-release Ambien CR, and the new Rozerem, from Japan's Takeda Pharmaceuticals, which claims to avoid the dangers of dependence and abuse. Next up, if approved by the FDA, may be Pfizer's Indiplon.

David Southwell, Sepracor's chief financial officer, isn't afraid of the competition. He sees potential for "growing the market" for sleeping pills since, by his estimate, only 10 percent of the millions suffering from insomnia seek pharmaceutical treatment. To help increase that market, Sepracor has dispatched a small army of 1,250 Lunesta sales reps, mainly to primary-care doctors' offices.

But while the newer sleeping pills are considered safer and less addictive than older sleeping aids such as Valium and Halcion, doctors and sleep experts worry that hyper marketing may encourage overuse.

Most sleeping pills are labeled for short-term use of a week or so, and even longer-use Lunesta has been tracked in studies for just six months.

But many sleepless Americans take the drugs for longer and then suffer "rebound insomnia" when they try to quit, says Allan Pack, head of the expanding sleep clinic network of the University of Pennsylvania Health System.

"It can be quite severe — it can be a long time before your own sleep system kicks in again."

Other experts note that sleep disorders are complicated. Before you pop a sleeping pill, say the experts, get a proper diagnosis.