Acute stress disorder can develop following a person’s exposure to one or more traumatic events. Symptoms may develop after an individual either experiences firsthand or witnesses a disturbing event involving a threat of or actual death, serious injury, or physical or sexual violation. Symptoms begin or worsen after the trauma occurs and can last from three days to one month.
It is estimated that between 5 and 20 percent of people exposed to a trauma such as a car accident, assault, or witnessing a mass shooting develop acute stress disorder. And approximately half of those go on to develop post-traumatic stress disorder.
The diagnosis of acute stress disorder was established to identify those individuals who would eventually develop post-traumatic stress disorder. The condition was referred to as "shell shock" as far back as World War I, based on similarities between the reactions of soldiers who suffered concussions caused by exploding bombs or shells and those who suffered blows to their central nervous systems. More recently, acute stress disorder came to recognize that people might exhibit PTSD-like symptoms for a short period immediately after a trauma.
Trauma has both a medical and a psychiatric definition. Medically, trauma refers to a serious or critical bodily injury, wound, or shock, and trauma medicine is practiced in emergency rooms. In psychiatry, trauma refers to an experience that is emotionally painful, distressful, or shocking, often resulting in lasting mental and physical effects.
In general, it is believed that the more direct the exposure to a traumatic event, the higher the risk for mental harm. Thus in a school shooting, for example, the student who is injured will likely be the most severely psychologically affected, and the student who sees a classmate shot or killed is likely to be more affected than the student who was in another part of the school when the violence occurred. Even secondhand exposure to violence can be traumatic. For this reason, all children and adolescents exposed to violence or a disaster, even if only through graphic media reports, should be watched for signs of emotional distress.