Sleep Apnea is a sleep disorder in which the person's muscles become so relaxed that the airways become blocked and the person has trouble breathing and actually stops breathing momentarily). These people tend to snore a lot. The big problem here is that the person is not getting enough oxygen. Each time they stop breathing their blood oxygen level drops until it gets so low it wakes them mometarily (usually not noticed by the sleeper). This cycle (stop breathing and then waking) can happen hundreds of times a night. In addition to dangerously low blood oxygen level, the person can't get enough slow-wave sleep so they usually feel tired and complain of poor sleep.