Three types of sleep apnea:
Obstructive, Central, and Mixed. Of the three, obstructive sleep apnea, often called OSA for short, is the most common.
Obstructive sleep apnea (the most common cause of sleep apnea) is caused by a blockage of the airway, usually when the soft tissue in the rear of the throat collapses and closes during sleep.
Central sleep apnea, the airway is not blocked but the brain fails to signal the muscles to breathe.
Mixed sleep apnea, as the name implies, is a combination of the two. With each apnea event, the brain rouses the sleeper, usually only partially, to signal breathing to resume.