1. The temporary stopping of breathing that takes place in some newborns and in some adults while they are sleeping: Apnea disrupts Harriet's sleep or, sometimes, she wakes up completely or goes into a shallow level of sleep.

Apnea involves the cessation of breathing either temporarily for a few seconds to a minute or two or for a longer period, which can possibly cause someone to die.

Since breathing is an automatic process controlled by nerve impulses in the center of a brain stem to the muscles in the chest that regulate lung expansions and contractions, prolonged apneas can occur if the brain stem is damaged by a stroke, by a transient ischemic attack (symptoms of stroke lasting less than 24 hours), or by a head injury.

Prolonged apnea can also occur because of certain drugs or as the result of airway obstructions, usually by food, drink, vomit, or a small inhaled object.

2. In zoology, a decrease or a minimal breathing in hibernating animals: Natural apneas take place when animals have periods of dormant (sleep) inactivities which usually occurs in winter with certain rodents, bats, and some large carnivores; such as bears.