Trauma psychologist Elizabeth Carll explained to CBS News Early Show co-anchor Jane Clayson that Post Traumatic Stress Disorder "is the feeling and anxiety response to a severe event such as a violent crime, disaster, or accident.
"Feelings are normal," she added. "Although they seem very extreme to us, everyone experiences those to a certain degree. If they last more than a month, we call it Post Traumatic Stress Disorder."
She mentioned that there is a psychological difference of survivors and victims from events of six years ago and two years ago.
"We think that five years down the road, many communities have moved on. But many of the symptoms of anxiety, stress, and even our memories and thoughts remain. They may be severe the first year. And five years down the road, after Oklahoma City, they are very much there still.
"They diminish over time, but anniversaries bring back the memory and they are real at the time we think of them."
Among the key symptoms of Post Traumatic Stress Disorder, Carll said, are "intrusive thoughts and memories. We can't get it out of our mind. [There are] flashbacks about anxiety and stress, feeling very jumpy, depressed, and sad, often feeling that we're going over the edge, maybe even losing it."
Symptoms may be more common than most people think.
"It's very common. When we lose someone in a car accident, for instance, a loved one, we all experience those feelings,"said Carll.
According to the trauma psychologist, there are ways of treating and getting help for post traumatic stress disorder.
"For many of us, having a supportive family, and having an opportunity to talk to people helps," said Carll, "and certainly professional help to deal with the stress and the anxiety."
"If it lingers on, it's important to get the help because it can change how we view the world down the road."
There is a difference with how men and women deal with PTSD, said Carll.
"Sometimes we think maybe women experience it more. That may be related to the fact that women talk about it more," she told CBS News. "Men hold it in. Sometimes it would appear they are not experiencing the same kinds of stresses, but they really are."
"I think we have all been and had the opportunity to attend many, many types of programs," said one Oklahoma City rescue worker. "We saw it coming, and really, I think, got over it in a hurry. I think there are some men and women that still hold things in, and it's all on a personal basis."