Up to 70 per cent of people will experience  a serious trauma during their lives. A  smaller figure, about 10 per cent, will fail to shake the horrific memory and go on to  suffer post-traumatic stress disorder, as  Court reporter PATRICK BILLINGS writes. 

IMAGINE a gun pointed at your head, being involved in a severe collision, surviving a flood or bushfire.

Up to 70 per cent of people will experience a serious trauma during their lives.

A smaller figure, about 10 per cent, will fail to shake the horrific memory and go on to suffer post- traumatic stress disorder.

The response to a traumatic event is fairly standard.

Most people will experience shock, anxiety, disturbed sleep and repeat memories of the experience.

In the case of an armed robbery "they may get an image of the assailant and an image of the gun might come up".

University of Tasmania professor Kim Felmingham said "these reactions are normal and to be expected".

It was when those reactions didn't go away that it could become a problem requiring intervention.

Professor Felmingham is a clinical psychologist who has been researching PTSD for more than a decade.

According to Professor Felmingham the brain decodes events during a traumatic episode that are tied to strong reactions, or "emotional arousal".

"Your body at that time is flooded with stress hormones - cortisol, noradrenaline - you're fighting or fleeing," she said.

"Now in that environment that memory at that time becomes associated with intense arousal."

When a PTSD sufferer encountered a similar situation, such as returning to work after a hold-up, it could trigger the same response experienced during the initial trauma.

There was no hard or fast rules about who was more likely to suffer PTSD.

Pre-existing mental health issues could increase the risk while the perception of an event was more influential than the "objective severity" of it.

Professor Felmingham has seen a gang member shrug off knife-fight injuries but the little old lady who gets her bag snatched might go on to suffer severe PTSD.

"Incidents that involve interpersonal violence are associated with more risk of developing PTSD than say a car accident or a natural disaster," she said.

PTSD could also develop in people who tried to avoid all things that reminded them of the trauma.

While that was an understandable response, if it was prolonged "you never ever get to learn [the trauma's] not going to happen again".

The brain also worked selectively, with sufferers only remembering the worst part of a traumatic incident.

For example, the victim in an armed robbery might only remember the gun against their head and thinking "I'm going to die", not the gun being lowered and the bandit walking away.

"Instead of remembering a coherent narrative that ends somewhere nice the memory of a trauma ... is much more fragmented and you tend to remember the worst bit of it," she said.

"So the treatments that we offer actually work directly with those memories to help you process [them] so you can create a coherent narrative and that actually reduces the fear and anxiety."

For more information visit the Australian Centre for Posttraumatic Mental Health at www.acpmh.unimelb.edu.au.

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