Acute stress reaction (ASR), also known as psychological shock, mental shock, or simply shock, as well as acute stress disorder (ASD), is a psychological response to a terrifying, traumatic, or surprising experience. The reactions may include but are not limited to intrusive thoughts, or dissociation, and reactivity symptoms such as avoidance or hyperarousal. It may be exhibited for days or weeks after the traumatic event. If the condition is not correctly addressed, it may develop into post-traumatic stress disorder (PTSD).