Acute stress disorder is an anxiety disorder that occurs within one month of a traumatic event. Trauma is defined as a stressful situation that causes intense fear. The stress often arise from a life-threatening or dangerous situation such as rape, mugging, combat, or natural disasters. Post-traumatic stress disorder is a similar disorder, but the symptoms occur months or years after the trauma takes place.

Acute stress disorder is characterized by dissociative and anxiety symptoms. Dissociation is a psychological reaction to trauma in which the mind tries to deal with the trauma by "sealing off" some details from conscious awareness. Dissociative symptoms include emotional detachment, temporary loss of memory, depersonalization, and derealization. Anxiety symptoms connected with acute stress disorder include irritability, physical restlessness, sleep problems, inability to concentrate, and being easily startled.

Diagnosis of acute stress disorder is based on the patient's history and a physical examination to rule out any physical problems. The key clue to diagnosis is a traumatic event within one month of the onset of symptoms. The diagnosis is supported by symptoms that significantly interfere with a person's normal ability to socialize or to work. Some symptoms of acute stress disorder result from biochemical changes in the central nervous system, muscles, and digestive tract that are not subject to conscious control. Symptoms last between two days and four weeks.

Treatment for acute stress disorder usually includes antidepressant medications and short-term psychotherapy. Acupuncture has been recommended as a treatment, and other alternative approaches include meditation, breathing exercises, and yoga. These alternative approaches may be helpful when combined with short-term psychotherapy.

Recovery depends on the severity of the trauma and how long it lasted. Other important factors include a person's closeness to the trauma and his or her previous level of functioning. Recovery is usually quicker when only a short time period has passed between the trauma and onset of symptoms. Immediate treatment and good social support improve the chances of a good recovery. If the patient's symptoms interfere with normal life and have lasted longer than one month, the diagnosis may be changed to post-traumatic stress disorder. Without treatment, a person with acute stress disorder is at increased risk for substance abuse or major depressive disorders.

Traumatic events usually cannot be predicted, so it is difficult to prevent acute stress disorder. However, professional help soon after a trauma might reduce the likelihood or severity of the disorder.