Though sometimes, the events of a story are really horrific and it's hard to forget about it. My mind would just morbidly keep going back, craving some kind of closure that the actual story could never provide. I usually come across this after reading or watching something very heavy or emotionally draining (e.g. after reading something like 17 sai. or Tsumi to Batsu: A Falsified Romance or watching Game of Thrones or Telltale Games: The Walking Dead).
I think one coping mechanism that I end up falling into is to daydream all sorts of elaborate fantasies about how it should have gone, i.e., fix-its. Ignoring any nagging doubts about it being "too unrealistic", "too good to be true", "Mary Sue", "wish fulfillment", etc. because it's my own brain, I can do what I want! Wish fulfillment it is!
If the work is one with a sizable fandom, I try to see if there are any fanfics out there that put such fix-its in writing. (e.g. this fanfic is a favourite Danganronpa fix-it of mine :P)
Some other of my coping strategies:
- Sleep it off
- Play something mechanical, such as Go or Tetris (apparently, Tetris helps with PTSD)
- Channel Zetsubou-sensei (a silly manga), and proclaim loudly, "I'm in despair! OOO has left me in despair!"
- Watch some stupid funny videos—laughing is good for mental health (I recommend "Whose Line Is It Anyway" clips and "You Suck At Cooking" videos)