Bear with me, I have difficulty sharing stuff like this, so if it's confusing, you'll know I actually put thought into it.
If something doesn't bother me right away, I keep it inside out of instinct, and don't, I guess let it out. I always, never fails, always assume that I'm over it, isn't going to bother me, and never will.. I'm always, wrong, I've been affected by some very minor details, from nasty calls, several months afterward. In once case, it was almost a year after a traumatic death, traumatic as in literally Trauma, of an infant; I was just sitting here, I think I was watching TV. I couldn't concentrate enough to tell you what caused it, or how I came to it, but I just bummed out real quick and started crying, as if the call just happened.
I refuse to CISD after any call, I'd probably even take a forced leave if I had to, to skip one. I never thought the first one I attended did anything, it took a few days for it to catch up to me. I just like to keep things to myself, and hope they dissolve on their own.
If asked for this advice, I'd be a hypocrite, I'd tell them to never keep things inside. Bottling things up causes a lot of bad things to happen, unless you have some way to release stress and chip away at what you've bottled up. Try a CISD, and if it still affects you, find something on your own that is a safe way to release your feelings.