To echo what has has already been said, these things can come back a while after the fact when you’re least expecting it.
I was first on the scence of a RTA about 20 years ago and didn’t think anything of it really, until about 5 years ago while on a first aid work course there was a picture on the slideshow that brought everything flooding back. I was asked to leave the room by one of the trainers who took me for a cup of tea and a chat after which I felt much better. I hadn’t realised but as that picture was shown I went a shade of green and just stared into the distance for a minute or so before someone pointed it out.
I hadn’t thought about the incident for years, and it didn’t trouble me at all at the time (quite the opposite, I felt really good about being there and able to help in some way, and the driver fully recovered) so even if you feel ok now, talking it over might help (either now or in the future)