I was diagnosed with GAD too and when my breathing got bad, I used what I knew and insisted on it being true and that helped me as well as learning to breathe better. I knew I'd been checked and there was nothing physically wrong with me so I "ignored" the symptoms as if they were just an annoyance like a gnat/fly and kept reminding myself I was still breathing and doing fine, hadn't passed out or anything, etc. I either played the "game" of trying to describe what my chest felt like in detail until I was sick of/bored with it or I distracted myself by starting to read a good book or do some other thing that used my head enough to get my mind off how I felt. Sometimes a routine that included a "treat" (lifesaver or small piece of candy or even my berry-flavored antacid or "French Vanilla" calcium supplement) often did the trick if it is close to bedtime. I look forward to whatever novel I'm reading before I go to sleep so do my whole asthma and get ready for bed "routine" and by the time I climb in to bed to read, I feel better.