Tens of millions of Americans snore loudly, most dismissing the disorder as an annoyance. But many snorers unknowingly suffer from obstructive sleep apnea, a potentially life-threatening disorder that often goes undiagnosed. Sleep apnea causes a person to stop breathing--for periods of at least ten seconds--hundreds of times a night. Most sufferers don't remember the incidents the next morning. Untreated, the syndrome is thought to cause high blood pressure, irregular heartbeat, stroke, depression, memory loss, and heart attacks, not to mention impotence. Studies have also found that fatigue from sleep apnea plays a major role in car accidents. Loud snoring, therefore, may be a signal to see a doctor. Otolaryngologist Kent Wilson, of the University of Minnesota at Minneapolis, suspended a microphone 24 inches above the heads of 1,139 slumbering men and women. He found that snoring that exceeds 49 decibels indicated a high risk of sleep apnea. Overweight people and men snored loudest, and 12 percent of the subjects topped 55 decibels, roughly the loudness of rush-hour traffic. "People who snore extremely loudly need to be taken seriously and treated medically," Wilson says.