When I was acute, I had lots of breathing symptoms, the type your having was one of them, for me, I new it was anxiety related because on the onset of all my panic/high levels of anxiety, I had, had a good check over.
From what I understand, when anxiety kicks in the lungs can expand, get larger, hence the feeling you can;t take any more air in, you have alot of air in there, hence not being able to take large breaths. Although this is harmless, it can be very scary if you don.t understand whats going on.
YOU WILL carry on breathing no matter what, your lungs are always on auto pilot, so to speak.
What I found help, was to breath out as much as I can... and then you automatically breath in, do this 2 times, more if you can, BUT, if it makes you feel dizzy, STOP.
Also what helped me was to understand that I am NEVER going to stop breathing, I AM in control, I learned all the breathing techniques, eg, learning to breath from the lower half of my tummy and any other techniques I could find, there are some threads on here, Mmm not sure where they are, not been active for awhile myself.
If you can.t find breathing tec, in here you can get the on the net.
I found them really good, they also helped me move forward;
I also bought a self hypnoses cd, which I listened to A LOT.
Is does go in time hun
Hope this has been of some help, even if its just knowing your not alone.
LO0VE JILL XXX