Positional apnea
Sleep apnea in which most pauses in breathing happen while lying on the back and become clearly fewer when lying on the side.
A little more detail
Under a commonly used definition, the supine AHI is at least twice the non-supine AHI. In more than half of patients with obstructive sleep apnea, apnea worsens when lying on the back; positional therapy is one of the treatment options.
Source: Omobomi O, Quan SF. Positional therapy in the management of positional obstructive sleep apnea: a review of the current literature. Sleep Breath. 2018;22(2):297-304. doi:10.1007/s11325-017-1561-y