rumination

noun

ru·​mi·​na·​tion ˌrü-mə-ˈnā-shən 

: the act or process of ruminating:

a

: the act or process of regurgitating and chewing again previously swallowed food

b

: obsessive thinking about an idea, situation, or choice especially when it interferes with normal mental functioning

specifically : a focusing of one's attention on negative or distressing thoughts or feelings that when excessive or prolonged may lead to or exacerbate an episode of depression