A medical disorder that causes a person to stop breathing for periods of time during sleep. Sleep apnea can be caused by airway blockages or brain signal problems. Those with sleep apnea may stop breathing dozens or hundreds of times a night, for 10 seconds or more each time. This causes the person to gasp for air, interrupting the normal sleep cycle and often preventing deep sleep. Since deep sleep is essential to good physical and mental health, those prevented from reaching that level of rest by sleep apnea may exhibit a host of symptoms from fatigue, poor concentration, irritability, and personality changes to the medical effects of lower oxygen levels that manifest themselves as high blood pressure, heart problems, stroke, and an increased risk of injury.