I can totally relate to your attack while shopping. I had that happen to me about 6months ago with my 4yr old son in tow. It was horrible, scary, and I thought I was going to pass out right in Meijer. I use caution while going out now, only do short shops alone, but I have gotten a little better.
I find what works best for me is.....breathing. (Breathe in for a count of 4, hold for 4, and let it out for a count of 4. In about 5 min you will feel so much better.)
If that doesn't help I go to klonopin. It relaxes me and helps me get through the worst situations. (Sometimes I cheat and take on even before I get to the store.)
I also suggest seeing a doctor or therapist too. Just so you can find out what's up.
I hope this helps you some, take care....
Dee