Post traumatic stress disorder (PTSD) has been recognized for last 15 years. According to 10th revision of the International Statistical Classification of Diseases and Related Health Problems the person with PTSD must have been involved in a definite traumatic event or events, which may have included actual or threatened death or serious injury. The person involved must also have felt very powerless at the time. There must also be a number of symptoms present involving:

• Intrusive memories or "flashbacks" of the events(s)
• Recollections of the trauma or Persistent avoidance of reminders of the event(s)
• Increased arousal (being constantly on the "lookout" for danger, increased heart rate, anxiety and panic, etc.)
• Feeling emotionally numb and experiencing a loss of interest in activities or other people.

These must be present for at least one month after the event. Clinical psychologists and other health care professionals use well-researched and established questionnaires and an interview to determine whether PTSD actually exists and how severe it is.