If someone has positional sleep apnea, most particularly obstructive (rather than central) sleep apnea, here's a simple intervention that may help.  Not everyone will tolerate this, and it may not eliminate all apneic episodes.  (But not everyone tolerates CPAP and other interventions either.)  Take a T-shirt or pajama top.  In the *middle* of the upper *back* sew a pocket that will hold a half of a tennis ball.  (Cut a tennis ball in half.)  Put the half-tennis-ball in the pocket and sew the pocket shut.  If one turns onto one's back, the discomfort caused the tennis ball will cause a shift in position to another sleeping position.  At first, this may cause multiple awakenings but, usually over 3-4 weeks, if one persists with this, it will "train" one to sleep in other positions and avoid the back position.  If the apnea is positional, this obviously will have no effect.