The more common of the two forms of apnea, it is caused by a blockage of the airway, usually when the soft tissue in the back of the throat collapses during sleep.
Unlike OSA, the airway is not blocked, but the brain fails to signal the muscles to breathe, due to instability in the respiratory control center.
This is a mixture of both obstructive sleep apnoea OSA (where there is a blockage or obstruction in the upper airway) and CSA (where no effort is made to breathe). Your doctor can help you understand more about this if you need to.