I struggled at first, too, and I'm still a newbie! I don't know anything about the technicalities of the machinery, but I do notice that breathing is a struggle if I'm tense. For example, the night I found out my uncle died, I was struggling for air for a couple of hours. I thought I had put my mask back together wrong after cleaning it. But it also occurred to me that it might be grief. I didn't use the machine for a couple of days, and when I went back to it, I could breathe fine.
Before the whole grief thing, I would say it took me a few days to adjust to the machine pulsing air at me on my exhale.
I didn't struggle, either, during my titration study, but I attribute that to the fact that a technician was at the controls, not a machine, and she didn't start changing the pressure until I was asleep.
A couple of things that I found comforting, and wish I had learned earlier:
1) you can still breathe if your mask is on but not hooked up to the machine.
2) your breath doesn't go back down the tube, so there's no way your germs can infect the hose, water, etc., and come back to re-infect you.