"Acute Stress Disorder (ASD) is characterized by dissociative symptoms (e.g. detachment, derealization, or amnesia) during or after exposure to a traumatic event followed promptly by symptoms of re-experiencing, avoidance/ numbing, and hyperarousal from two days to a maximum of four weeks after the traumatic exposure. While not the only disorder seen acutely after exposure to traumatic events, ASD is quite common. The American Psychiatric Association and the U.S. Department of Veterans Affairs Office of Quality and Performance have published Practice Guidelines for the treatment of ASD."
Center for the Study of Traumatic Stress: http://www.centerforthestudyoftraumaticstress.org