Firstly, you have done the right thing. Don’t bottle it up, it is always best to speak about something that affects you if you feel comfortable to do so. What you have seen will have a lasting impact on your life, I’m truly sorry that you had to suffer this awful tragedy.
I suggest, you contacting your GP, and ask for counselling, you might not feel you need it but even by talking about it will sometimes help, all people are different and deal with life changing incidents in different ways.
If you love driving, you need to remember this was an extreme one off, and try to get back behind the seat as soon as possible, the longer you are away the more you might not want to return.
Also, remember this could have an affect on your family, and you must remember you are not at fault, you can relive it over and over in your head a million times, there would of been no way you could of changed the course.