Post-traumatic stress disorder (PTSD) is an anxiety disorder that develops after a traumatic event.
PTSD has also been called shell shock or battle fatigue.
The exact cause of PTSD is unknown. PTSD is triggered by exposure to a traumatic event, but not everyone who experiences a traumatic event will develop PTSD.
Situations in which a person feels intense fear, helplessness, or horror are considered traumatic.