Hi PhilosophicalPinkQuelea3435,
I also have a problem with my chin dropping when I sleep. I was told by the tech at the sleep lab that it happened at the end of the night (not all night long), so I think my issue is mild.
The first chin strap and nasal air pillow interface that I tried did not work for assorted reasons. After 30 days of experimenting with that combination, I ordered a different interface, that has a built in chin strap. That worked for me, but I think what I need was a "gentle reminder" vs. firm support.
If your DME provides customer support, I would start by contacting them, for advice.
I have been told that sometimes people can learn to keep their mouth shut while sleeping.
Good luck. I hope you get other responses and that you find this site helpful. I have only been using CPAP for 3 months and I found this site a helpful resource as I adjusted to using CPAP.