I just want to say that even though you feel embarrassed you should be proud of yourself for going to the store, that's a hell of a lot more than I could do at times. I used to have absolute meltdowns about ordering lunchmeat if that makes any sense. What I do if I'm feeling especially vulnerable is wear earphones and listen to a radio show or music while I'm shopping.

If you keep forcing yourself to do the things you're terrified of (like the store and people judging) it will get better. Next time instead of SIing, try dunking your face in ice cold water and holding it under for as long as you can. Sounds silly but you'd be surprised how effective it can be to switch off the bad thoughts.