Only hurting yourself

Here is the deal, I know that a person must set appropriate boundaries, I am definitely on board with that, but how do you go about effectively dealing with old hurts that happened a long time ago but are bubbling up now?  What gives?  Why does this stuff happen when you are losing weight?  Maybe its chemical?  I don't know.

I'm going to a meditation class tonight.  I'm really hoping that helps because for the past week or so I've been having what I call Dementor attacks.  I feel just despondent over stupid stuff that just doesn't matter anymore and that I thought I had forgotten about.  This old gunk just is not important or relevant at all.  I've done the work of forgiving the person who did it at the time (a very tuff bully I had for 4 years.) I've heard that you are sent the lessons that you can handle, but how was I supposed to handle that?  I had no skills at the time at all.  I just don't get how that was supposed to help me as a person.  Also, if we are supposed to learn the lesson of forgiveness I understand that one, but how do you meld both concepts, understanding the bullying individual and not rewarding the bullying behavior?  And, why would such a "lesson" be popping up now?