Freud says trauma is an external event or excitement strong enough to affect normal psychic activity and defence mechanisms. ICD-10's definition of trauma is: “an event that is outside the range of usual human experience and that would be markedly distressing to almost anyone”.

But what is the role of pre-morbid mental health status and the reason for different presentations in survivors of the same event?

The vulnerability theory applies here. Vulnerability in psychic function originates from previous experiences, particularly in childhood when the internal world is still developing and external experiences are able to shape it.

Therefore we can summarise that quantity and intensity of an external event would determine whether or not the survivor would be affected by that incident, whereas the quality of interaction between this event and previous experiences of person (vulnerability) would determine the presentation and, particularly, the long term consequences of that traumatic event.

In the first 48 hours, the survivor needs and wishes to find something or someone he can perceive, even temporarily, as offering primary maternal care. For many this will be a pressing need to return home. After the first 48 hours, people feel urge to start talking about incidence. These are considered as normal stress reaction. But in some survivors (who are vulnerable), they may remain in the first stage of regression for longer or feel overwhelmed by unmanageable aspects of their experience and show prolonged symptoms known as PTSD. Both of these conditions need outside help and treatment.