So if you are relatively new to PAP therapy, don't be too hard on yourself. This is a process. Let's face it, getting your face into a mask every night, is not a natural thing to do and your mind won't simply be accommodating to the new and strange way that you turn yourself in.
Add the flow of air hitting your nostrils (and mouth if you wear a full face), , will also feel like you are trying to get a shuteye with your head stuck out the window of a speeding car on the highway...It is simply not something that your mind will be ready to accept, unless you have a very special character.
So if you are wondering how you will ever get used to falling asleep wearing the contraption, don't sweat it too much because getting used to wearing the mask and feeling that air hitting your lungs, is only a part of the journey

I'd say that if you are somewhere between a very docile and accommodating character to an extreme one who just can't get used to doing something new (on a regular basis), you will need to give mask wearing about 6 continuous months to get used to, and then just as you get used to wearing your mask without it leaking like a sieve all night and keeping you awake, you will notice that you need to start tinkering with your machine, if you are targeting a low AHI and a good night asleep.
This process (also known as titration) also needs a good few months to get used to. In my case this part didn't take that long because I am on an ASV equipment so my machine pressures are set wide open and it works on demand for my CSA. All I had to do was to get used to being automatically ventilated during those events when I stop breathing for 20, sometimes 40 minutes at a time.
If you persevere, you will end up with perfect therapy for your condition, whether you are suffering from OSA or CSA.