Sleep apnea is a cessation of breathing for at least 10 seconds while asleep. This may occur because the upper airway is blocked or malformed, or because the respiratory muscles stop functioning.

Most people experience occasional sleep apnea, but frequent recurrences disturb sleep and can cause daytime sleepiness and loss of attention. Since sleep apnea deprives the body (and brain) of oxygen, severe cases can lead to hypoxia. Sleep apnea can be life-threatening in infants and old people.