When an individual stops
breathing while asleep, he or she must be suffering apnea, a kind of sleep disorder.
There are two reasons for apnea attacks. One reason is that the brain fails to send a "breathe" signal to the diaphragm and other
breathing muscles, thus causing breathing to stop. The other reason is that muscles at top of the throat become too relaxed, allowing the windpipe to partially close and thereby forcing the breathing muscles to pull harder on incoming air, which causes the airway to completely collapse. During an apnea episode, the oxygen level of the blood drops dramatically, leading to the secretion of emergency hormones. This reaction causes the sleeper to waken in order to begin breathing again.