Could some one explain to me what a posttraumatic stress disorder is?

Post trauma symptoms: Posttraumatic stress disorder (pstd) is the development of chronic (over1 month duration) symptoms following a life-threatening trauma.The person re-experiences the trauma in nightmares, flashbacks etc.They avoid situations that recall the trauma. Emotions are numbed.When exposed to reminders of the trauma, they are too arroused, startled with angry outburts.Their families suffer as does work.