Hi PG,
I am sorry to hear of your anxiety and symptoms...I know how challenging, scary and confusing those feelings are!
A couple of things pop out at me reading your post. One is the classic progression of worry to symptom. In line at the store, you first had the thought, and then came the feeling. This is very typical and indicative of anxiety. Here is a link that explains the cycle really well.
Health Anxiety- The Super Scanner
http://www.get.gg/docs/SuperScanner.pdf
The other thing that struck me was how well you did at talking calmly to yourself with your mantra, and shutting down the panic...well done!
Practicing this more and more will bring you progress. We have other coping skill ideas in our Resources, so be sure to check them out and put them into practice as well.
Keep looking for ways to manage your anxiety...whether it be medication, therapy, self help...or a combination of all of these.
The key is finding what works for YOU!
We will be here cheering you on along the way, so keep posting!
S.C.