Posttraumatic stress disorder (PTSD) was an anxiety disorder that could develop after exposure to one or more terrifying events that threatened or caused grave physical harm.
It was a severe and ongoing emotional reaction to an extreme psychological trauma. This stressor may involve someone's actual death, a threat to the patient's or someone else's life, serious physical injury or threat to physical or psychological integrity and overwhelming psychological defenses.
In some cases, it could also be from profound psychological and emotional trauma, apart from any actual physical harm. Often, however, the two are combined.
PTSD was a condition distinct from traumatic stress which had less intensity and duration and combat stress reaction which was transitory. PTSD was also recognized in the past as railway spine, shell shock, battle fatigue, traumatic war neurosis or post-traumatic stress syndrome (PTSS).
The diagnostic symptoms included re-experience such as flashbacks and nightmares, avoidance of stimuli associated with the trauma, increased arousal such as difficulty falling or staying asleep, anger and hyper vigilance. Per definition, the symptoms lasted more than 6 months and caused significant impairment in social, occupational or the other important areas of functioning which are problems with work and relationships.
In the series
In the Resident Evil 5 Viral Campaign, Chris Redfield appeared to be suffering from a form of PTSD after Kijuju. He appeared to have a flashback each time that a bright light flashed him. In Resident Evil 6, Chris suffered from post-traumatic amnesia after the death of several men in the City hall under his command during a mission in Edonia. Piers Nivans found him in a bar, heavily intoxicated and lacking any memory of his men, the BSAA or even bio-terrorism in general.