I side with anniereborn and Hawaii Jake on this. Not sure the others are talking about the same thing. It’s like fears and phobias; everyone has fears, but not everyone has phobias.
But even if we limit the use of “trigger” to some sort of clinically severe reaction, I don’t think trigger warnings should be required. I would hope that educators would exercise good judgment about the material they present, though, and warn their students when there is a good chance that someone in the class might be adversely affected by it. (E.g., if a teacher is showing Saving Private Ryan and knows that there are veterans in the class.)