Oh, Stella, I am sorry to hear that. I must admit, I have suffered many "shame storms" in my day. And they do seem to come out of nowhere and at the oddest times....like walking down an innocuous hallway or something like that.
I have never learned a particular technique to help with them, but sometimes I can think my way out of them.
1) Did I actually do anything for which I should be ashamed? Would I think someone else should be ashamed if they did the same thing?
2) If I did do something wrong, have I worked to apologize for my behavior? If so, did the person(s) forgive me? If the person did forgive me then I should be able to forgive myself.
3) Breathe!