Post traumatic stress disorder (PTSD) is a psychological condition that some people develop after experiencing or witnessing a terrifying event. People with PTSD often relive the trauma through nightmares and flashbacks, have difficulty sleeping, feel detached or estranged, and/or have problems with anger or depression. People with PTSD often feel stressed and irritable, have problems concentrating, and may startle more easily. Some people never develop PTSD, for some it's a temporary reaction, and for others it becomes a life-long problem.