G'day ,
I have been in a similar situation that you have been about 5 years ago and it was a first hand experience for me .i was asked to take counseling but I chose not to. Now looking back into it I believe it is totally upto the individual as how one perceive these kind of accidents and what their age is when they have witnessed or been into one.
I am not even sure if I am at a position to advise because of the fact I don't have a medical qualification. However I would suggest to take the time out and be with your family or your loved ones or even take a holiday to south east Asia for a bit of a adventure or just get on the horse te next day and don't let it get to you
Hope this helps
Oz