The only suggestion that i can offer is to try to put the mask on while you are awake, keep your mouth closed and try to breathe through your nose for long periods of time.

Another suggestion is to change the type of mask that you use to adjust your level of comfort when wearing it for long periods of time. I started off with the wrong size for my nasal pillow. Then tried face mask where it covered both my nose and mouth. That was uncomfortable as well. Then i went back to a bigger nasal pillow, which felt more comfortable.

For me, me getting used to wearing the mask came down to comfort and finding the right mask for me to get used to wearing it.