Sleep apnea is a condition that affects how you breathe when sleeping. During sleep, normal breathing can be interrupted for 10 seconds or more hundreds of times during a single night. Untreated sleep apnea prevents you from getting enough deep, restorative sleep. Without enough deep sleep you may be sleepy, lack mental sharpness and be less productive. Long term health effects can be serious, including weight gain, high blood pressure, heart disease and diabetes.