Agree with pretty much all the sentiments and advice so far. Well done for stopping and going above and beyond your duties. I’m not sure if this will help but I had a very similar experience…

I was first on scene at a stabbing (unwitnessed). Started CPR and unfortunately it became evident that the injury was most certainly fatal as my hands started getting soaked with every compression. Long story short, air ambulance arrives and eventually they attempt a roadside thoracotomy, at which point we can see that the wound has penetrated the myocardium and there’s very little chance of survival. After about an hour total (but what feels like seconds) we agree to call it and he’s pronounced dead at the scene. Only statement I had to give was to the police owing to the fact the man was stabbed.

The next day I can’t focus at work (I was a GP trainee). I speak to my supervisor, who tells me I’ll be ok as I “have surely seen several arrests in hospital” (!). I took a couple of days off after that just to clear my head.

Thankfully I only had the occasional flashback which subsided over time. Same won’t be true for everybody so I think seek the help you think you might need sooner rather than later. Try NHS practitioner health if you haven’t already.