CNN  —  For a potentially serious medical condition, it’s remarkable how few people know they have obstructive sleep apnea (OSA). OSA, in which a person’s upper airway collapses, causing irregular breathing, is the most common sleep-related breathing condition. One study estimated well over 900 million adults between 30 and 69 years old may have it worldwide, though as many as four in five moderate-to-severe cases are undiagnosed. Left untreated, it can increase the risk of high blood pressure,