True about post traumatic stress disorder is:

Ref: Synopsis of Psychiatry: Kaplan & Sadock. 10th edit ionExplanation:Post traumatic stress disorder (PTSD)It is a psychiatric disorder following a major stress or traumatic event as the name implies.It is one of the psychiatric disorders where stress plays a direct and determinant role for the evolution of symptoms.Such disorders are classified as follows:1. Adjustment disorder, where the stress is common and not a catastrophic one, e.g., strain in the interpersonal relationship.2. Acute stress reaction/disorder and PTSD. where the stress is rare, unbearable and catastrophic in nature, e.g., rape, accident, floods, tsunami, war. Note that a person may be a victim or even be a witness to develop such disorders.Acute stress disorder (ASD)It is diagnosed when the signs and symptoms occur within 4 weeks after the stress.Symptoms should subside within 2 days to 4 weeks.If the symptoms occur after 4 weeks and/or persist for more than 4 weeks, then a diagnosis of PTSD is made.Both ASD and PTSD share same symptoms and etiopathogenesis except for the fact of onset and duration of symptoms.The symptoms areIncreased arousal as evidenced by sympathetic overactivityRe-experiencing the event fin dreams as seen in children, in wakeful state where it takes the form of flashbacks) with or without cues (cues are anything which remind the stressful event) Persistent avoidance of stimuli associated with the trauma (like detachment from usual activities and known people).Though nightmares do occur in PTSD. they are not specific for this disorder.