Acute stress disorder or acute stress reaction is a psychological condition that occurs in response to an extremely traumatic stressor. This usually last a minimum of 2 days to a maximum of 4 weeks and must occur within 4 weeks of the trauma. If symptoms are present for longer than 4 weeks the diagnosis is changed to Post Traumatic Stress Disorder. Symptoms experienced are similar to PTSD and include numbness or detachment and decreased or absent emotional responsiveness. Derealization, depersonalization and inability to recall the traumatic event.