do you ever tell people they are triggering you.

it may seem a strange question, but a valid one- do you tell people don't talk about that, it triggers me, or do you just don't tell them?

I was put in this situation today actually.

someone I was with started talking about something that happened to someone else, and that thing that happened to someone else, also happens to be something that triggered me a few months back (their were other reasons as well, but that was the main one)

anyway I went all quiet and she asked me if I was okay and I'm like yes of course, and she's like.. I hope I didn't trigger you, and I'm like no... no, of course not- you're fine

difficult sometimes as I honestly feel I need to tell them

what do you do