Some media exposure to tragedies keeps children informed about the environment they live in, but it would be wise to monitor their exposure and, after a point, put away the newspapers and turn off the TV, she said.

Parents should not become alarmists, but if a child's behavior is out of the ordinary because of such an event for a matter of days, then it's time to consider professional help. "I would be concerned if my child didn't to go to school for three days because of something like this," Wilson said.

Adults, meanwhile, have a variety of reactions to an episode of violence, but their greater maturity and life experience may offer them more emotional resilience, according to Jed Ericksen, associate director of adult services at Valley Mental Health.

It is perfectly normal for an adult who has endured a traumatic incident to become preoccupied with what happened, have visual images of it, think it through over and over, feel insecure and fearful and perhaps avoid places that the individual associates with the event.

"These are understandable and natural reactions," Ericksen said.

However, if things do not improve in six months or so, and the reactions from the event are interfering with the individual's life, then it would be a good idea to seek professional help, he said.

Often, adults can do nicely with "informal" help from family, friends, co-workers or others who permit the adult to vent, but a few need professional help — and they should not feel embarrassed in asking for it. "You don't have to be considered emotionally crippled to have those kinds of feelings."

In a few cases, people can develop post-traumatic stress disorder, which involves such painful, frightening symptoms that it interferes with the person's day-to-day life. This is treatable, often with a combination of therapy and medication.

University of Utah psychiatry professor David Tomb said the people hiding in closets and back rooms at Trolley Square Monday evening had "very severe exposure" to trauma, even if they never even saw the shooter.

But typically only 5 percent five to 10 percent of these people will go on to develop full-blown PTSD or severe depression.

Of those people, about half will usually still have PTSD — significant enough to make them afraid to go into shopping malls again or drive down 700 East past Trolley Square — three years later.

"They may still hold a job, and most do and seem to perform fairly well," Tomb said, "but they know they're spending their lives on the razor's edge."

The people who react to trauma with either PTSD or severe depression often have a genetic history of anxiety or depression. For the 90 to 95 percent of people who don't react so severely, they'll likely have weeks or months of minor levels of PTSD symptoms, Tomb said. "It will be an experience they'll never forget, and they may have trouble shopping in malls, but they won't feel like their whole world has turned upside down."

For the rest of us, who watched the aftermath at Trolley Square, a small percentage will have minor symptoms of post-traumatic stress Tomb said. In rare cases, some people will develop significant symptoms, Tomb said — the same way some children were too frightened to go to school anymore after the Columbine shootings in 1999, even though they lived thousands of miles away.

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