A new dad in his early 40s, Steve Volk was on the verge of a personal and professional crisis. He was depressed, overweight, and struggling to handle his responsibilities as a husband and father. After undergoing a sleep study, Volk was diagnosed with sleep apnea, a medical condition that afflicts tens of millions, though roughly 80 percent go undiagnosed. For people with sleep apnea -- a sleep disorder in which breathing is interrupted during sleep,...