Chances are, however, they're not staying asleep for the time it takes to go through the deep, restorative stages of sleep needed to feel refreshed in the morning. That's why, in many cases, how you feel during the day is the best indicator of whether you might have a problem.
This was the case with Virginia Arguello, 44, a medical transcriptionist in Hayward, Calif. In her mid-30s, Arguello began falling asleep during her morning drive to work, even after a full night's sleep.
"I was scared to get in the car by myself," she says. "I was ashamed because I didn't have energy to play with my kids and I couldn't concentrate at work. But I have a thyroid problem, so I just blamed my sleepiness on that plus the fact that I was raising three daughters and working full time."
Luckily something else tipped off her doctor: Arguello had recurring nightmares of being underwater, unable to swim up and reach the surface. "I would wake up gasping," she says. "My husband complained that I snored and gasped for air."
When she was diagnosed with sleep apnea, Arguello received a continuous positive airway pressure (CPAP) machine to keep her airways from closing while she slept. "After just the first night, I remember the difference being so dramatic, like night and day," she recalls. "I never realized how much energy I'd lost and how sleep deprived I'd become, until I had one truly good night of sleep."