Obstructive Sleep Apnea (OSA), the most common type, occurs when there is a blockage of the airway, which is caused by the relaxation of the muscles in the back of the throat, causing the airway to narrow or close. When this happens, you cannot get enough air, the oxygen levels in your blood decrease and you wake up (although you do not remember it), so that you can breathe again.
In Central Sleep Apnea, there is no blockage in the airway. However, the brain does not signal the muscles to breathe. In simple words, you do not breathe for a short period of time. As a result, you cannot get to sleep or stay asleep.
