NIH - Medical Encyclopedia: Post-traumatic stress disorder

"Post-traumatic stress disorder is a psychiatric illness that can occur following a traumatic event in which there was threat of injury or death to you or someone else. … (PTSD) may occur soon after a major trauma, or can be delayed for more than six months after the event. When it occurs soon after the trauma it usually resolves after three months, but some people experience a longer-term form of the condition, which can last for many years. … People with PTSD re-experience the event again and again in at least one of several ways. They may have recurrent distressing dreams and recollections of the event, a sense of reliving the experience (referred to as flashbacks), and/or become very distressed around the time of events that symbolize the event (such as anniversaries)."

Posttraumatic Stress Disorder and Health Status: The Veterans Health Study. (J Ambul Care Manage. 2006)

"The association of PTSD with health status was substantial, suggesting that the burden of PTSD is at least comparable to, and may be worse than, that of depression. Mental health treatment alleviated some of this burden. The potential impact of PTSD on health status should be more widely recognized."