Also, have they tested TSH, T3 & T4. If your thyroid is out of balance this can cause anxiety problems.
Have they also done a thyroid ultrasound to check for nodules?
Unfortinately, probably not. It's not out of the question, but it usually works the other way: panic attacks subside, and then the gastro symptoms. The key to making the first happen is finding out the reason for your panic attacks. I've been there and done that, so I know how you feel. I also know how tempting it is to get on anti-anxiety meds. Problem with these is that they can (and often do) make the GERD worse, because they relax the LES. Better to go the talk-therapy route which, while possibly longer, is far more sustainable.
Good luck.