Hi Samantha,
Perhaps if you seek professional help for Post Traumatic Stress Disorder would be more acceptable for your parents. Then, the psychiatrist will do the proper diagnosis. It is not uncommon for people that had accidents have PTSD and maybe they do not see PTSD as something they could have caused to you. Do you have any source of income independent from your parents? That may make the difference, at least you can use your own money if they refuse to pay for the treatment .
Good luck with everything!