This disorder can develop after exposure to a terrifying event that could have caused (or did cause) physical harm. It is considered a severe and ongoing emotional reaction to an extreme psychological trauma. The threat of physical injury or death is so severe that the person is unable to cope. A wide range of symptoms accompanies this condition.
Patients with PTSD who have accidents or injuries may be at increased risk for problems with chronic pain. Studies show poor outcomes for patients with PTSD after whiplash injuries. Their coping mechanism just isn't able to handle trauma or an event that someone else might consider mild.
A psychologist and a physical therapist working together may be able to help your brother regain a sense of self-efficacy (can do attitude) and coping strategies. Treatment may not be needed right away. But if you continue to see questionable behaviors, attitudes, or actions, don't hesitate to make the suggestion for a screening exam. Early intervention can make a difference.