Acute stress reaction (also called acute stress disorder, psychological shock, mental shock, or simply shock) is a psychological condition arising in response to a terrifying or traumatic event, or witnessing a traumatic event that induces a strong emotional response within the individual. Acute stress reaction (ASR) may develop into delayed stress reaction (better known as PTSD) if stress is not correctly managed. ASR is characterized by re-living and avoiding reminders of an aversive event, as well as generalized hypervigilance after initial exposure to a traumatic event. ASD is differentiated from PTSD as a disorder that precedes it, and if symptoms last for more than one month, it will develop into PTSD. It can thus be thought of as the acute phase of PTSD.