In the wake of a tragedy such as the movie theater shooting in Colorado, those who live wonder why they survived when others didn't.

"You're happy that you're alive, but then again, you're sad because you know certain people died," said Eric Hunter, a witness to the shooting last week in Aurora. "You know children died. You wish, you know, why not me instead of them? You just feel bad."

Jennifer Seeger, another witness, said, "I heard that a 6-year-old was shot. And I was just thinking the entire time, you know, 'How come I got so lucky?' ... I'm 22 years old. I've lived my life. You know, as far as that goes, I would love to take a bullet for that 6-year-old to live their life."

Among the 12 victims of the shooting were three men who were fatally wounded while saving their girlfriends. Jansen Young is one of the women who survived because her boyfriend, Jon Blunk, 26, shielded her from bullets.

"I look at that and know that I would do the same thing if the tables had been turned, and if I would have been able to take the bullet for him, I would have," Young told CNN affiliate KTVX.

When a person survives a traumatic incident in which others died, especially loved ones, it's common to feel guilty for living. Survivor guilt can be an immediate response to a tragedy, and the extent of the feelings depends on the individual, said Russell Jones, a psychologist at Virginia Tech who helped counsel victims at the school after a shooting rampage in 2007.

It's important to understand what the survivor guilt means for the person, said Melissa Brymer, director of terrorism and disaster programs at the UCLA Neuropsychiatric Institute in Los Angeles. A lot of times, she said, it's an expression of grief and loss.

People may feel that someone else got hurt because of them. Maybe they could have been at the event but, by coincidence, didn't go. Or it may be that someone did something heroic, perhaps even dying to save that person's life, and "They're appreciative of what happened, but they're struggling with: They are alive, and their loved one isn't," Brymer said.

For some people, survivor guilt is just part of working through complex feelings after experiencing a traumatic event involving deaths and a way of mourning. But it may become all-consuming and impede functioning.

Sitting back and taking time to process the event can help survivors cope, Jones said. Seeking support from friends, family and community or faith leaders can help an individual work through difficult feelings.

But if there's lingering guilt and anxiety, Jones recommends consulting a mental health professional. A survivor may experience symptoms of post-traumatic stress disorder and depression that requires formal treatment.

"If they're having changes within their behaviors or in their emotions or with their relationships with others, then we want to make sure that people get help," Brymer said.

Unfortunately, people who need help often don't seek it, Jones said.

"So often, there's stigma attached to getting help from a mental health professional," Jones said. "Therefore, they go without seeking treatment, oftentimes until they reach a breaking point."

About 8% to 15% of people who experience trauma develop severe PTSD symptoms that persist and require professional help, Jones said. With support, people generally do well, he said.

Classic symptoms include intrusive thoughts, flashbacks and nightmares. People may avoid anything that reminds them of the event and have difficulty paying attention. It may be paired with depression and suicidal feelings.

These symptoms can lead to full-blown PTSD over time, especially if a person has a history of mental illness. Previous trauma, stress, loss of financial stability, and grieving the loss of family and friends are also risk factors, Jones said.

There are several treatment strategies that have been shown to help people with survivor guilt and PTSD symptoms, he said.

Exposure is a central element of these strategies. Getting people to talk about the event and assimilating the event into everyday living are key, Jones said. Therapists may also take the individual back to the setting where the tragedy occurred and allow the person to express his or her thoughts, feelings and emotions.

Therapists can teach clients relaxation and breathing skills to alleviate anxiety and to emphasize positive thoughts.