What could this be?

So in November of 2016 my older brother had a near fatal overdose off of heroin. My dad found him in the garage in the middle of smoking a cigarette, hunched over and unconscious. My dad and brother dragged him downstairs and my dad revived him after 10 minutes of doing CPR. My dad and brother said his body was cold and he wasn’t breathing and couldn’t even feel his heartbeat. Well after years of addiction, that was his wake up call to finally get help. He found a new job and after awhile stayed in a halfway house and met a great girl. They live in ocean city Maryland now and he is getting married soon. But for some reason I’m still not over his overdose. I think that was probably the most traumatic thing that has happened in my life and I always picture myself finding him that day and him not making it because I was the one that was supposed to find him that day. I was supposed to come home from school and take him to work and he was supposed to be home alone. Thank god I didn’t find him or I would’ve been more traumatized than I already am. But after this happened, my family was really different for a long time. Everything is kinda normal now, everyone has their family issues, but why am I picturing these scenarios still? Of me finding him and stuff like that. It’s been almost 3 years he’s been sober and it’s like I’m still anxious about it. The first time he went to rehab for drugs was when I was 12 and whenever he overdosed I was 18. I watched him fuck up his life for all those years so maybe that messed me up a bit? I’m not really sure. It’s just a scary thought.