I've had a cpap for 11 or 12 years. I've never used it on a plane, though. I saw one used on a CX flight a couple of weeks ago, as well as a KLM flight the week before.
I usually just stay mostly awake for the 30+ hour trips I seem to take. Needless to say it takes a few days to get back to normal.
Still, better than falling asleep driving which led to my first and only sleep study. My machine alarmed 'red' the last I returned from Asia. It's done this before as well as a few yellow alarms.