Obstructive sleep apnea syndrome (OSAS) is a debilitating sleep and breathing disorder defined as the cessation of breathing for 10 seconds or more (an apnea) at least five times per hour of sleep. During sleep, the body's muscles relax, which can cause excess tissue to collapse into the upper airway (back of the mouth, nose and throat) and block breathing. When breathing is interrupted by an obstruction in the airway, the body reacts by waking enough to start breathing again. These arousals may occur hundreds of times each night but do not fully awaken the patient, who remains unaware of the loud snoring, choking and gasping for air that are typically associated with obstructive sleep apnea. Obstructive sleep apnea sufferers never get "a good night's sleep" because repeated apneas and arousals deprive patients of REM and deep-stage sleep, leading to chronic daytime exhaustion and long-term cardiovascular stress.