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. It should not be confused with the unrelated circulatory condition of shock/hypoperfusion. 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.