Mightymouse,
Congratulation on being cancer free for 9 years! As far as the sleep apnea, many head and neck cancer patients suffer from this mostly from radiation, and although some only temporarily during or soon after treatment, some do permanently. I know I did during my various treatments, and thereafter for extended periods, and wouid sleep on an incline on my side, and in a recliner chair mostly sitting up, although it may be difficult or nearly impossible for you to do so. There is a specific body pillow to help with this as just using more pillows or sleeping on an incline bed may not be as ideal.
That’s exactly how I would awaken several times during the night, trying to grasp my breath. For me, it was a matter of time before it corrected itself.
I have no other suggestions I can recall, besides seeing your doctor, but maybe a SLP, Speech and Language Pathologist, for exercises to help strengthen the soft palate, if that is possible.
Good luck with everything!