Post-traumatic stress disorder (PTSD) is a type of anxiety disorder that's triggered by a traumatic event. You can develop post-traumatic stress disorder when you experience or witness an event that causes intense fear, helplessness or horror.
Definition, symptoms, causes, risk factors, complications, preparing for your appointment, tests and diagnosis, treatments and drugs, coping and support, and prevention.
Mayo Clinic
http://www.mayoclinic.com/health/post-traumatic-stress-disorder/DS00246