@hemant Posttraumatic stress disorder (PTSD) is a syndrome resulting from exposure to real or threatened serious injury or sexual assault. The signs and symptoms of PTSD appear to arise from complex interactions of psychological and neurobiological factors. Studies have found alterations in the amygdala, prefrontal cortex, hippocampus, and anterior cingulate, and corpus collosum as well as altered functioning of the hypothalamic pituitary axis (HPA).
Signs and symptoms
Symptoms of posttraumatic stress disorder (PTSD) include the following:
Persistent re-experiencing of the event: intrusive thoughts related to the traumatic event, nightmares or distressing dreams, persistent or recurrent involuntary memories, dissociation (including flashbacks) and intense, negative emotional or physiological reaction on exposure to reminders (traumatic triggers)
Avoidance of traumatic triggers or of thinking/talking about the experience
Negative alterations in cognition and mood: inability to recall important aspects of the trauma; persistent negative beliefs and expectations about oneself, others, and the world; inappropriate blaming of oneself for the trauma; exaggerated negative beliefs about the consequences of the trauma; persistent negative emotional state (sadness, horror, guilt); a paucity of positive emotional experiences; loss of interest or participation in important activities; and detachment from people.

Increased arousal or reactivity: irritability, problems with sleep or concentration, increased startle reaction, increased vigilance for potential danger, self-harming acts, or recklessness
One cannot diagnose PTSD until one month has passed since the traumatic incident. Acute stress disorder, which has similar symptoms, is diagnosed during the first month.

Diagnosis
Diagnosing PTSD in adults, adolescents, and children older than 6 years of age using the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) [1] requires a certain type and level of traumatic event, a combination of required symptoms, and the absence of exclusionary criteria.
A) Causation: The victim was exposed to actual or threatened death, serious injury or sexual violence in one of four ways:
Directly experiencing the traumatic event(s)
Witnessing, in person, the event(s) as it occurred to others
Learning that the traumatic event(s) occurred to a close family member or friend
Experiencing repeated or extreme exposure to aversive details of the traumatic event(s); this does not apply to exposure through media such as television, movies, or pictures
B) The traumatic event is persistently re-experienced:
Nightmares
Intrusive thoughts of the traumatic event
Flashbacks
Marked emotional distress when exposed to traumatic reminders
Strong physiologic reaction when exposed to traumatic reminders
Children may re-experience the event through repetitive play.
C) Avoidance in one of two ways:
Avoidance of thoughts, feelings, or conversations associated with the event
Avoidance of people, places, or activities that may trigger recollections of the event
D) Negative alterations in cognition and mood. Two of the following:
Inability to remember an important aspect of the event(s)
Persistent and exaggerated negative beliefs about oneself, others, or the world
Persistent distorted cognitions about the cause or consequences of the event(s)
Persistent negative emotional state
Markedly diminished interest or participation in significant activities
Feelings of detachment or estrangement from others
Persistent inability to experience positive emotions
E) Hyperarrousal: Two of the following:
Irritable behavior and angry outbursts
Reckless or self-destructive behavior
Hypervigilance
Exaggerated startle response
Concentration problems
Sleep disturbance
F) The duration of symptoms is more than 1 month
G) Disturbance causes clinically significant distress or impairment in functioning
H) The disturbance is not attributable to the physiological effects of a substance or other medical condition