Post Traumatic Stress Disorder
It might help to explain what PTSD is.
Without wanting to go into too much detail, PTSD is a diagnosis of anxiety, hyper-arousal or depression brought about by either an overwhelming traumatic event, (rape, severe crashes, bereavement, etc.), or by longer periods of trauma, (childhood sexual abuse, neglect, etc.).
In the face of such traumas, a high number of people (up to 50%) will experience ongoing effects, naturally, and this seems to be a way of the mind recovering from the effect of the trauma.
This will drop off in time, and gradually many people will stop suffering.
A significant minority, though, will continue to suffer from stress as a result of the trauma, and the amount of suffering will be effected by the amount of trauma in the first place, their ability to find support, how young they were when the trauma happened, and how well they process stress related to their personal history and possibly genetic influences.
This is termed Post-Traumatic Stress Disorder, or PTSD.