Good questions. I had been and am still a very motionless sleeper. Rolling around in bed would often trigger some horrific spasms, causing full chest contractions and some shortness of breath. So, my body learned to stay-put, usually in a fetal position.
One thought postulated from my son was that I'm breathing more deeply and the flexure of rib cage might be aggravating nerve and tissue around forming/bridging osteophytes. I'm leaning this direction. Muscle relaxants not helping much, other than helping me nod off in a chair after I have to bail out of bed.
Oddly, my 0300 trip to the loo (frequent, but not always) hasn't happened since I began using the APAP.
DX AS 2016. DX DISH Syndrome 2000. Humira, SOMA as needed, oils (black spruce, wintergreen, cypress, peppermint, lavender). Severely intolerant to NSAIDs.