I get this when I'm particularly anxious.
I was told once that it's not the breathing in that's important but the breath you exhale, as this apparently relaxes you
The exhale always does feel more relaxing doesn't it?
I read that if you put your awareness in the physical feeling in the tip of your nose.
I also learnt a technique on a cbt course called castle breathing, which I always forget to use, but it is effective, and it goes:
Inhale for two
hold for two
exhale for two
hold for two,
repeat... and you can see how this would also be visually similar to the shape of a castle.
I think it would be what I would use if my panic attacks manifested themselves in that way, but mine manifest in feeling like I am going to faint or be sick, or really awkward, legs go to jelly, having to sit down.
If this happens when I am trying to stand up for myself it makes me more vulnerable to verbal abusive types, but sorry to stray off the thread.