The absence of breathing.

Sleep apnea is a common sleep disorder characterized by brief interruptions of breathing during sleep. Episodes usually last 10 seconds or more and occur repeatedly throughout the night. People with sleep apnea will partially awaken as they struggle to breathe, but in the morning they will not be aware of the disturbances in their sleep. The most common type of sleep apnea is obstructive sleep apnea (OSA), caused by relaxation of soft tissue in the back of the throat that blocks the passage of air. Central sleep apnea (CSA) is caused by irregularities in the brain’s normal signals to breathe. Most people with sleep apnea will have a combination of both types. The hallmark symptom of the disorder is excessive daytime sleepiness. Additional symptoms of sleep apnea include restless sleep, loud snoring (with periods of silence followed by gasps), falling asleep during the day, morning headaches, trouble concentrating, irritability, forgetfulness, mood or behavior changes, anxiety, and depression. Not everyone who has these symptoms will have sleep apnea, but it is recommended that people who are experiencing even a few of these symptoms visit their doctor for evaluation. Sleep apnea is more likely to occur in men than women, and in people who are overweight or obese.