 The muscle tone of the body ordinarily relaxes during sleep, and at the level of the throat, the human airway is composed of collapsible walls of soft tissue that can obstruct breathing.Mild occasional sleep apnea, such as many people experience during an upper respiratory infection, may not be significant, but chronic severe obstructive sleep apnea requires treatment to prevent low blood oxygen (hypoxemia), sleep deprivation, and other complications.Individuals with low muscle-tone and soft tissue around the airway (e.g., because of obesity) and structural features that give rise to a narrowed airway are at high risk for obstructive sleep apnea.