I'm sorry you were too ill to be shopping, it's tough to do what needs to be done when not feeling up to it.

I'm not sure you were scapegoated. I think your pain must have caused you to take personal offense at the woman's need to have her groceries bagged?

It's unfortunate that you felt calling her names was an acceptable response to her being there. She was in front of you, and therefore, imo, rightfully being served first. Learning to wait in line was something I learned in kindergarten.
(Actually at home first, I am from a big family )

I hope you will be able to work on your anger with your T. Pain makes it a short distance between being able to cope with a situation, and striking out at strangers.