The way I gauge if something is worth mentioning is if it is affecting my day to day life now. If something happens that triggers me, it is worth bringing up in session because I am going to therapy so that my day to day functioning is better. I think keeping things in perspective (worse things have happened to other people, etc) is a good thing to do outside of therapy, but if it's bugging you then it is totally appropriate to bring up in session. Some people find things upsetting that others would just shrug at, the point is that it upset you and is still rattling around in your head. I would bring it up.