If you are getting a dry sore mouth in the morning when using a nasal mask then my bet is you are a mouth breather when you sleep. You should try a full face mask. They can be harder to adjust to but you will never get a good night's sleep if you are breathing through your mouth.
Having read the statistics on those after bariatric surgery becoming alcoholics I'm not surprised by some of this but it certainly scares me so please guys look after yourselves and your bodies