I hunted through the internet searching for a clear definition of PTSD (post-traumatic stress disorder). Some sites described this disorder in such a brief manner even I struggled understand it, then other sites explained in such detail it was way over my head. Discovering this site and link @ National Institute of Mental Health came closest to the definition for me.
What is Post-traumatic Stress Disorder (PTSD)?
When in danger, it’s natural to feel afraid. This fear triggers many split-second changes in the body to prepare to defend against the danger or to avoid it. This “fight-or-flight” response is a healthy reaction meant to protect a person from harm. But in post-traumatic stress disorder (PTSD), this reaction is changed or damaged. People who have PTSD may feel stressed or frightened even when they’re no longer in danger.
PTSD develops after a terrifying ordeal that involved physical harm or the threat of physical harm. The person who develops PTSD may have been the one who was harmed, the harm may have happened to a loved one, or the person may have witnessed a harmful event that happened to loved ones or strangers.
PTSD was first brought to public attention in relation to war veterans, but it can result from a variety of traumatic incidents, such as mugging, rape, torture, being kidnapped or held captive, child abuse, car accidents, train wrecks, plane crashes, bombings, or natural disasters such as floods or earthquakes.
More on this article @ NIMH