Tommy M:
That sounds quite familiar, do you think it could have anything to do with the feeling of being "in control" of the breath?
If so, I've experimented with it a bit in the past and managed to get quite a good level of control over the breath. What I ended up realizing was that it was just more fabrication, "I" don't breathe, the body does and it knows what it's doing. It ends up leading to something like a jhana, if I remember rightly, as the focus required on the breath is more one-pointed, but I don't know if it's worthwhile or useful in terms of practice really.
I did have dreams where I wouldn't be able to breathe through my nostrils, and there would be a huge panic, until finally I'd manage to finally take a breath.
And I remember one or two times when I was short of breath (deep end of a pool, and when someone sat on my head while wrestling on a bed when I was younger), and the fear is similar... so maybe there is a desire to control the breath so that doesn't happen?
I don't want to control the breath, though, I'd rather let it do its thing. The reason I don't like letting that sharp in-breath happen when I do this is cause it seems to diminish the fear, but not in a way of its gone forever now, but rather in a way of sublimating it/turning it into something more subtle and unconscious, but still ready to pounce at a moment's notice.
I don't think learning how to control my breath would help. I can do that anyway.. no? I'm not sure I follow what your advice is.