The relevant term for what you describe in psychology circles is "rumination" in...

rkalla · on May 25, 2011

I am, thank you for that. Looked it up on Wikipedia ( http://en.wikipedia.org/wiki/Rumination_(psychology) ) and it sounds spot on.

Originally I found the cow-cud-chewing article, and that sounded less spot on, but then I found the "mental rumination" link :)

eavc · on May 31, 2011

Cud-chewing is the etymology of the psych term, actually. Regurgitating the same thing over and over...

Glad you enjoyed the read. It's something I deal with personally as well.