There are certain things that I absolutely can't watch. Horror and thrillers for sure. Anything involving blood or serious amounts of suspense. Fantasy violence (sword fights/magic battles) is usually not an issue, though. I just assumed that it was just as triggering seeing something on screen as it would be to have it brought to mind in other ways. Like one thing that's very triggering for me in the media is anyone drawing blood with a knife. I have to close my eyes, even for on-screen pinpricks. For things that aren't triggering, I just assume that since I have PTSD, I have a lower emotional tolerance for suspense than I otherwise would. I think of it like the stress-cup analogy, only with the stress associated with suspenseful movies, which would usually be completely dispersed by the movie's cathartic ending. But if it overflows before the movie ends, well, I have a tough time.
(If you like good, serious stories, and are looking for something sweet/interesting to watch, I was enchanted by "Phoebe in Wonderland," which is about a young, obsessive girl who lands the lead in her school's production of 'Alice in Wonderland.' It asks some important questions without being too suspenseful.)