Mark,
I won't say just relax and let whatever happens at the Dr happen. I had the same problem about even having the conversation. I looked up some info on Panic attacks (do the test on this site, it will give you a pront out to take to your Dr). I took the info with me to the doc and he was elated that I had researched it. I found out he has several patients with this problem andhe was very understanding. This problem has become more prevalent in the last few years and the stigma it might have once had is gone! Also, remembering that your doctor works for YOU might give you that mental edge. You ahve hired him to help manage your health...that is what he is there for. If he/she appears to not understnad, ask for someone else that does or make some calls from the phone book until you find one that will help you. THEY WORK FOR YOU!!!!
Good luck, hang in there...and know that you will feel a million times better once you've gone in and gottenback out of the dr's office. You'll be that much closer to getting better.
I'm rooting for ya!!!