i would try and focus your mind on something different so you arent thinking about "breathing" all the time and let your body just naturally breath
but i DO know how you feel, sometimes when i have a panic attack (rarely) i feel like i take a deep breath and its like it just doesnt feel like that breath satisfied me enough so i try and breath again and i feel like i cant catch my breath...its a freaky feeling and that brings on the anxiety and panic.
if your strong minded enough just step outside of what your going thru and read a book or watch a dvd or go for a walk or call a friend to take your mind off of it.
if your really worried about it then you could always call up your doc to have them check your blood pressure and listen to your lungs

That will definately reassure you!