It was never the same for Mark after his traumatic experience.
Mark Oliver from Northampton had just started his new job as a Wall Street attorney when terrorists attacked the Twin Towers.
He was on the 57th floor of the North Tower when the plane hit the building above his office.
Eight years on he is living with Post Traumatic Stress Disorder which has lead him to write about his experiences.
He hopes that sharing what he's been through will help others.
"The symptoms of Post Traumatic Stress Disorder like anxiety, breathlessness and insomnia remain with you for life. They can be lessened and you can learn how to deal with them, but they are never going to completely go away."
Everything from crowded places to a particular telephone ring would trigger a panic attack.
He's been unable to go near a petrol station - simply because of the smell.
After the plane hit, jet fuel poured down through the building.
It became clear to Mark that he wasn't able to travel on the sub-way.
"The building was vibrating in the impact and afterwards when I was walking along the street, any vibration from an underground train became a trigger for horrendous flashbacks."
It's like a river that floods. After the flood has subsided the river may flow along a different path. The brain ends up functioning slightly differently
The nightmares and the lack of sleep started to affect his life which resulted in him leaving his job.
This is when he started doing research on PTSD.
He said PTSD doesn't just apply to war veterans and people caught up in war zones.
"It can apply to victims of crime, how they're dealt with by police and by their family and friends. It can also be triggered by someone saying you really need to be getting on with your life."
Mark hopes his research will help anyone suffering from the disorder as well as relatives and friends who need information and advice on how to deal with someone close to them who has PTSD.
In his quest for information he has come to learn that knowledge and understanding helps manage the symptoms and has helped him come to terms with the horrific memories he has to live with.
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