I use to suffer rumination quite badly. An anti obsessive medication greatly helped as did some CBT. A big help though was changing my behavior. I made an effort not to do those things which encouraged and exaggerated the rumination. Namely seeking out the source and things like researching it, looking it up, etc. Oh I get the urge to do so still and it is tough not to engage in such behavior but CBT has given me skills to help me avoid doing so.