Have you talked with the doctor about this specific symptom, to rule out asthma or something like that?
If yes -- I'm with you. I have this building panic sort of symptom where I start to feel chest tightness or shortness of breath... And the more I think about it the worse it gets. This can go on for hours or days and had me in the doctor's/urgent care more than once. Sound familiar?
An idea-- what I try to do is stop whatever it is I am doing and rest my brain, either distract (watch TV, call someone on the phone, exercise) or dump (nap if I can, meditate). This helps in some but not all cases. If I get really freaked I break out the peak flow meter. I am asthmatic so I have one of these to monitor how much air I'm taking in vs. my best average. however since the anxiety started I find it useful for distinguishing between 'real' asthma or shortness of breath and anxiety. When I'm panicky, my peak flow will be at or approaching normal even if i feel really uncomfortable.
I know how uncomfortable that "can't breathe" feeling can be and how it is when it won't go away. It is also difficult, but you can train yourself to recognize the difference between panic and problem... That worked for me, the two are slightly different feelings now. I hope these ideas help a little bit.
I have panic attacks as well if you are on meds make sure you are taking them correctly. I have tried to over do it and it just makes things worse. One of the effects of panic attacks is feeling like you cannot breath. Don't over think it relax and find a light hearted distraction.