Night two was worse than night one with the CPAP. I don't know why, but I just couldn't get to sleep. I dozed a little but mainly tossed and turned and got up twice for the bathroom in two hours (I was right, the tubing can reach the ensuite so I don't have to unplug anything, I just walk in there with it all still on!). The air pressure on the CPAP starts quite low but after a while it slowly ramps up (that's why they asked me how long it takes me to get to sleep) and after a two and a half hours I felt like Darth Vader.
I think the problem was just that I couldn't stop thinking about the process. Breathe in, breathe out. Breathe in, breathe out. Keep mouth closed. Breathe in, breathe out. I tried telling myself I was doing nose breathing meditation but that didn't seem to help. So shortly after 1am I took it off and went to sleep quite quickly.
I'm not discouraged (although I admit I was hoping for instant success), I know it can take weeks to get used to. So I'll just keep putting it on every night. Try to get through the days without biting anyone's head off. Write a little every day even if I don't want to and I'm only producing rubbish that will be edited out later. Find things to enjoy other than food.