As far as I know the only proven way to deal with RSD is through talk therapy (whoa, there's a thread about that rn, one I'm ignoring) and like the usual coping mechanisms people talk about like mindfullness and cognitive reframing and such. I deal with it pretty bad too and Ive had the same thought and there's not like a medication for it or anything (though anti-anxiety stuff can help) so you just gotta learn coping mechanisms the best you can. I totally understand how hard it is to deal with in the moment. It hits me on like a daily basis. But yeah its a learn how to cope thing. And I'm not there yet myself. I still let it out on other people and react bad to rejection, and it can be very not pretty.