LOTS OF PEOPLE snore-in fact, almost half of all adults do. Most of the time it's just an annoyance for the people who are trying to sleep next to them. But sometimes it's a sign of something more—a breathing disorder called sleep apnea.

"In the U.S., about 10% of the adult population-which is roughly 30 million people-have sleep apnea," says Atul Malhotra, MD, a professor of medicine and a sleep medicine specialist at the University of California, San Diego. "Worldwide, about a billion people have sleep apnea."

The disorder is increasing in prevalence because of the obesity epidemic and the aging population.

"More awareness and better technology for diagnosing sleep apnea also contribute to the rise in cases," says Dr. Malhotra.

The problem isn't the snoring, but the reason behind it. The most common type of sleep apnea, called obstructive sleep apnea (OSA) is caused by weakened throat muscles relaxing too much during sleep, causing the airway to narrow or close. That leads to snoring plus shallow breathing and long pauses between breaths, followed by gasping for air. And when breathing is affected this way at night, the brain isn't getting the oxygen it needs, and the body isn't getting the sleep it needs either.

Snoring is the most obvious symptom, but people who sleep alone, or with partners who are very sound sleepers, may not even know that they snore, pause their breathing or gasp. (People who wear recent versions of the Apple Watch can turn on sleep apnea notifications.)