Apnea is a medical term used to describe a temporary cessation of breathing. It is usually caused by a blockage in the airway, such as during sleep, and can be a sign of a more serious underlying condition. Apnea can also be caused by a decrease in oxygen levels in the blood, or by an obstruction in the respiratory system. Treatment for apnea typically involves lifestyle changes, such as avoiding alcohol and smoking, and using a CPAP machine to help keep the airway open.