What I had to teach myself to do was asnswer each of the "Remember?" questions with "And?"
"So what?"
"and the point of bring up this now is...?"
I treat my brain precisely the way you want to, except I challenge it to answer me, give me proof that there is a reason for dragging up the crap other than to just reinforce the bad status quo and make sure I stay low and "safe".
"Remember the time my teacher made fun of my math in front of the class?"
Yep. So? The point is? She's dead now. I'm not. That's all that matters.
"Remember that mom hacks at you even when the others are at the house?"
Yep. She's a nasty wench when she has that mood. And? Her grief, not mine. What does that have to do with now?
I bet your memories never bring up the good things that happen, do they. Instead of trying to get your brain to shut up, try to get it to spew out some of those as well. I'm pretty sure they are there. HUGGGSSSSSSS!