nightmarenorm

Does the effect happen as soon as you go to sleep and enter a nREM phase or does it wait until the REM phase?

Do you have the ability to lucid dream, and if so, what are the effects between it and the disorder?

Considering that you are able to make it to the REM phase, it seems highly plausible that staying conscious while you dream will either alleviate the problem or give you the option of managing your breathing while getting the sleep that you need.

Have you heard of lucid dreaming?

The ability to remain conscious while you're sleeping may be a very valuable skill for you, and it would be interesting to know the effect it has on your condition.