Posttraumatic Stress Disorder (PTSD) is an anxiety disorder that can develop after exposure to a terrifying event or ordeal in which grave physical harm occurred or was threatened. blank">National Institute of Mental Health, US National Institutes of Health It is a severe and ongoing emotional reaction to an extreme psychological trauma. This stressor may involve someone's actual death or a threat to the patient's or someone else's life, serious physical injury, or threat to physical and/or psychological integrity, to a degree that usual psychological defenses are incapable of _coping. PTSD is a condition distinct from Traumatic stress, which is of less intensity and duration, and combat stress reaction, which is transitory. The condition has also been recognized in the past as shell shock, traumatic war neurosis, or post-traumatic stress syndrome (PTSS).