Trauma & Post-traumatic Stress Disorder (PTSD)
Post-Traumatic Stress Disorder arises when people are involved in a dangerous event, suffer a sudden shock, death, or serious injury/assault. Most people recover with time and have no ongoing distress related to their trauma. PTSD is diagnosed when people experience continual flashbacks, recurring bad dreams, or intrusive thoughts for longer than a month.
Resources on traumatic events available here.