Robert Prieto sometimes snored so loudly he woke his wife, Maggie. She'd lie in bed, waking up a dozen times as he did. If the snoring didn't wake her, his kicking legs did. And she noticed that he sometimes stopped breathing for brief periods.

Night-shift work is notoriously hard on sleep habits, and Prieto often worked the graveyard shift at a water reclamation facility, monitoring equipment. But his lack of sleep and subsequent fatigue were becoming increasingly serious.He was always tired, it seemed. He developed what he now refers to mildly as a "bad attitude" and "intolerance." He was grumpy.

And he was desperate for a solution.

That's how he ended up at the Salt Lake Regional Hospital's sleep disorder clinic, one of several sleep disorder clinics along the Wasatch Front. There, technician Will Spriggs hooked him up to electrodes and monitors, then sent him to bed in a spacious, comfortable bedroom on the hospital's second floor. Using polysomnography, which plots brain waves, eye and limb movements, respiration and other body activity, center staff hoped to determine if Prieto had a sleeping disorder and how to treat it.

The "if" is a big question, according to Dr. Kevin McCusker, one of the clinic's physicians.

Snoring doesn't always mean sleep apnea, a condition where breathing stops periodically during sleep. Apnea does, however, usually mean snoring. And fatigue has a multitude of causes, not all of them sleeping disorders. So patients are screened before they come into the clinic. They are asked about medications, illnesses and extra stress. They are asked about their symptoms. Their spouses - who often know more about what a patient does while asleep - are questioned, too.

Prieto did, in fact, have a diagnosable sleep disorder: obstructive sleep apnea, caused by his body's difficulty keeping his airway open while he slept, according to Dr. Joseph A. Schoenhals, another clinic physician.

The disorder can be created anatomically by big tonsils, the tongue blocking the airway, an enlarged uvula. Sometimes the airway collapses because of lost tone or excessive body weight.

Changing positions can help. But if the condition is bad enough, the oxygen level falls. And breathing can stop for long periods - even minutes. Usually it wakens the sleeper, sometimes many times an hour. It's not a prescription for a restful night. And daytime fatigue follows.

Performing and feeling well requires sleep. And there are stages required to having a refreshing sleep that some patients never get to, according to McCusker.

"We're seeing a virtual epidemic of sleep disorders nationally," he said.

Among the most common:

- Obstructive sleep apnea. It's impossible to get good, refreshing sleep when you startle dozens of times a night to take a breath, as Prieto did.

Nearly 30 million Americans have some form of sleep apnea. Most people with apnea do well with CPAP, a device that delivers continuous positive airway pressure, hence the name. The continuous positive airway pressure keeps the airway open, preventing apnea and the ensuing lack of oxygen and subsequent fatigue.

That was Prieto's diagnosis. He said the device, which is cumbersome but portable, has allowed him to turn around the quality of his sleep completely.

Excessive weight contributes to apnea approximately 50 to 70 percent of the time, Schoenhals said. So treatment may also include referral to nutrition and exercise counselors.

In some cases, surgery may be required. For instance, in a uvulaplasty, a surgeon burns or shaves off tissue to open an airway. That's "great for snoring," Schoenhals said, "but it's about 50 percent effective in terms of treating sleep apnea."

In the most severe cases, a tracheostamy is performed.

- Narcolepsy. Describing it as "undesirable sleepiness at inappropriate times," the American Sleep Disorders Association lists four common symptoms, but excessive daytime sleepiness is usually the first and the worse. Cataplexy, sudden and brief losses of motor control, is another symptom.

The condition, which effects 250,000 Americans, is particularly serious when someone falls asleep while driving or operating machinery.

Treatment includes a combination of medication, behavior treatment and management of the patient's environment.

- Restless leg syndrome. Contrary to myth, it's not a psychological or emotional problem. It appears as a "creepy, crawly" sensation in the legs (sometimes the arms) when they are sitting or lying still, especially at bedtime. It can make it hard to sleep.

It can also wake someone from sleep or create restless sleep, leading to fatigue, anxiety and depression.

A third of restless leg syndromes have a hereditary cause.

- Periodic limb movement disorder. Unlike the above problem, these movements are involuntary. While many people with the disorder function fine, the results can be devastating.

The condition is most common in people who have kidney disease or narcolepsy. Some medications also increase frequency of movement.

Treatment of either disorder consists first of seeing if there's an underlying cause that can be dealt with. Medication is sometimes prescribed. But the most common treatment involves improving sleep hygiene (see accompanying box).

- Parasomnias. They include "disorders of arousal" like sleepwalking, sleep terrors and confusion. They usually occur when someone is in a mixed state, "awake enough to act out complex behaviors but is still asleep and not aware of or able to remember these activities," according to the American Sleep Disorders Association.

Most parasomnias are considered a more mild sleep disorder than apnea or narcolepsy, troublesome but not dangerous. But they, too, can lead to fatigue and sleep deprivation, which bring their own problems.

Sleep paralysis, the experience of waking with a feeling that the body's muscles are paralyzed, is one parasomnia. It's common in people with narcolepsy but can affect others, including those who are sleep deprived. It's terrifying but not physically harmful.

There are dozens of other disorders as well. Only a skilled professional diagnostician can determine if fatigue is caused by an actual disorder.

A sleep disorder can generally be diagnosed with one night at a clinic. But when no disorder is found, the patient shouldn't be disheartened, McCusker said. "There's a lot of power in a negative study. We've had patients who were convinced they had apnea and a study showed no significant apnea."

That forces patients to look at other causes for insomnia or fatigue.

"Insomnia's often related to stress," McCusker said. "A patient may have to resolve that stress or develop coping skills."

Doing that can, literally, change all aspects of life for the better.