It is not uncommon for a person who has been involved in a serious accident to suffer from PTSD, experiencing constant fear of driving in general and feeling that they are just about to find themselves in a similar accident again, and that there is not much they can do to prevent it. This fear can be debilitating, and interfere not only with a person's ability to drive, but also focus and sleep.
Typically, successful treatment of PTSD will include both, medication to alleviate the anxiety symptoms as well as psychological counseling to rebuild the person's confidence and rational outlook on the surrounding environment.