Researchers estimate roughly 30 million Americans have sleep apnea, yet as many as 80 percent of cases go undiagnosed. But there’s also a psychological reason sleep apnea flies under the radar: People adapt. And because sleep apnea doesn’t cause pain, its warning signs are easy to chalk up to stress, aging, or just being busy. “Feeling tired despite eight hours of sleep is a serious symptom of sleep apnea, and this needs to be looked into,” says Bijoy E. John, M.D., a sleep specialist and founder of Sleep Fix Academy in Brentwood, Tennessee. That said, snoring doesn’t necessarily mean sleep apnea, and not everyone with apnea snores.