For the survivors of the Las Vegas shootings, overcoming emotional wounds may be just as tough as recovering from their physical injuries.

The psychological fallout is likely to hit countless others — doctors, nurses and bystanders who treated them, along with eyewitnesses to the nation's worst mass shooting. Some of the victims and others may be affected long term and experience symptoms of post-traumatic stress disorder.

THE AFTERMATH

Fear, anxiety and reliving the experience are all common emotions in the days and early weeks afterward. That's considered a normal response to a traumatic event. These symptoms must persist for more than one month for before a diagnosis of PTSD to be considered likely.

"It's considered a psychiatric issue if your alarm system stays on instead of shutting itself off," said PTSD expert Dr. Frank Ochberg, a Michigan State University psychiatry professor. He has studied mass killings and helped create the International Society for Traumatic Stress Studies.

PTSD & THE BRAIN

PTSD can cause changes in the brain that lead to hallmark symptoms, including recurrent flashbacks and a heightened sense of anxiety that interferes with daily life. Normal sounds that mimic shooting — a car backfiring, a balloon popping — may trigger panic and intense fear that can be disabling. In PTSD, a region deep within the brain called the amygdala, which helps regulate the fight-or-flight response and how the body reacts to fear, becomes overactive. The result includes release of stress hormones at inappropriate times. Increased heart rate, blood pressure and panicky feelings may occur when there's no real threat to safety.

WHO'S AT RISK?

People who are physically injured in shootings, other violence or accidents are among those who may develop PTSD. It's most common in bystanders nearest to the attack and people related to or emotionally close to victims.

Some studies suggest women are more vulnerable than men and that genes or pre-existing anxiety or depression also may increase the risks.

Research shows PTSD is particularly common among people exposed to mass shootings versus other types of trauma, with rates as high as 90 percent reported in some studies.

TREATMENT

PTSD is typically treated with psychiatric counseling and sometimes medication including antidepressants or anxiety-reducing drugs.

Counseling can include repeatedly exposing patients to symbols of the attack, perhaps including revisiting the shooting scene, accompanied by a therapist who can help them learn to moderate their reactions.

Self-help including physical exercise and talking with others about the attack and resulting fears can also be beneficial.

RECOVERY

Some studies suggest full recovery may take as long as three years, or longer for those who never receive treatment. Ochberg said it's important not to stigmatize people who develop PTSD and to recognize it as an injury, not a weakness. Research shows the lifetime risk for developing PTSD is about 10 percent of U.S. women and 5 percent for U.S. men, he noted.

PTSD "can affect anybody and by and large people return to normal eventually," Ochberg said.