Given your past experience with the mental health profession, I think walking into a mental ward would certainly be a trigger. Backing out of going to see him again is understandable. As I understand SI, (which I may not grasp the concept) it is a coping mechanism (albeit a unhealthy one) some people turn to when their feelings become unbearable, to search for distraction or relief. If you were going to do SI again, it was likely going to be because you had trouble coping again. Anything that drives you to your level at which you do that, I would call a trigger or stresser.

I don't know if that helps, but I think I get where you are coming from.