Post traumatic stress disorder develops after someone is exposed to an extremely traumatic event. The event may be recent, such as a car accident or physical assault, or it may have occurred in the past, such as childhood sexual assault.

Reactions of grief, shock and anger are normal after traumatic events. However, people with post traumatic stress disorder experience severe, prolonged and intrusive reactions that dramatically affect their daily life. These may include intrusive thoughts or images of the traumatic situation that are as distressing, or more distressing, than the original event. Often people begin to avoid reminders of the trauma, including places or similar situations.