In San Diego County, Scripps Clinic operates one of the most prominent sleep labs at its Green Hospital in the Torrey Pines Mesa area. Patients stay the night and their sleep patterns are observed.

The lab at the Green Hospital looks like a cross between a high-tech data center and a hotel. It has four rooms designed to look like hotel rooms, with beds, nightstands and paintings. The air temperature is kept a little on the chilly side. There are no clocks or television sets or telephones, though people can bring whatever they want.

After arriving, usually around 7:30 p.m., patients are attached to various instruments to measure brain waves, chest and stomach movements, muscle tone, heart rhythm and oxygen level. Two technicians are on hand to monitor the four patients, said Dr. John Cronin, a sleep specialist who is certified by the American Board of Sleep Medicine.

Sleep apnea shows a telltale breathing pattern that you don't have to be a doctor to identify, Cronin said: The monitors that measure chest and stomach movement go flat, followed by large spikes in activity that slow down. Oxygen levels also drop, sometimes precipitously.

The stress of that oxygen deprivation takes a major toll on patients' bodies, Cronin said.

"I tell them it's kind of like going to Mount Everest -- repeatedly -- going up and down, up and down."

Age makes the symptoms worse, because older people have less reserve capacity.

"A 20-year-old man may have very severe sleep apnea by oxygen level, but because he's got so much cardiac and lung reserve, they make it through," Cronin said.

A related point: Apnea is a chronic condition.

"You don't just have it for a year, and then it goes away," Cronin said.