Similar happened to me about 15 years ago, and it still bothers me. Mine was out of the blue though, nobody had shared anything remotely violent or gory in the team. One guy decides to share a 'funny' video with a subject line of 'always search your detainees' or something. A guy gets seated in a room by a cop, asks for some water, cop leaves, guy sits for a moment, then pulls out a handgun and shoots himself in the head. I had headphones on and still remember the sound of his last 'exhale' after dying. Fucked me up for a while.
In short, don't stand for this shit. It's no joke how much it can affect you if you aren't desensitised already, especially if you aren't expecting it.