Post Traumatic Stress Disorder (PTSD)
PTSD can develop following exposure to or threatened exposure to one or more traumatic events. The event(s) cause intense fear during which the individual may feel like they (or someone very close to them) are about to die or experience serious harm. Traumatic events go beyond daily stressful events and can include: physical and sexual assault; accidents and road traffic accidents; birth trauma; natural disasters; witnessing someone being badly injured or killed; experiencing war and torture.
People experience a combination of the following symptoms: (i) Re-experiencing symptoms including unwanted thoughts and memories of the trauma, flashbacks, and nightmares; (ii) Avoidance symptoms such as avoiding talking about the trauma, avoiding thinking about it or feelings associated with it, and avoiding reminders of the trauma such as people, places or activities; (iii) Negative changes in thoughts and mood such as blaming self or others, feeling isolated or experiencing difficulty remembering aspects of the trauma (iv) Hyperarousal symptoms such as being overly alert or watchful and feeling jumpy.
More details about PTSD are provided by NHS Choices.