http://www.dictionary.com/browse/dwelling - dwell = to linger over, emphasize, or ponder in thought, speech, or writing

http://www.bbc.co.uk/news/magazine-24444431 - "Rumination: The danger of dwelling. The UK's biggest ever online test into stress, ..., has revealed that rumination is the biggest predictor of the most common mental health problems in the country. A bit of self-reflection can be a good thing, say psychologists. But just how serious can it get when introspection goes awry and thoughts get stuck on repeat, playing over and over in the mind? "