Are you taking any medications? There are some medicines that make you "forget" to breathe. I thought I was a little nuts, because I never thought about this being possible, but I noticed it only started when I started taking a particular medication. I told the doctor, and he changed the medicine. End of forgetting to breathe. I still thought it might have been just me, since I'd never heard of this. Then one day at lunch, a co-worker said she'd been taking a medicine that made her forget to breathe! My loud "Yes!" sort of startled her and I explained my experience, that I'd never heard of that from anyone else, and I had been worried because I didn't know what would happen if I went to sleep and forgot to breathe. She said, "You wake up!"

I know this isn't the same thing you're describing, my point is just that medications can do weird things to you.