Anger. Crying jags. Nightmares. They’re all normal reactions for survivors of the bombings at the Boston Marathon, and witnesses to the mayhem.

Kaitlyn Greeley burst into tears when a car backfired the other day. She’s afraid to take her usual train to work at a Boston hospital.

“I know this is how people live every day in other countries. But I’m not used to it here,” said Greeley, 27, a technician at Tufts Medical Center who was on duty Monday when part of the hospital was briefly evacuated even as victims of the blast were being treated.

Those psychological aftershocks are the often invisible wounds of disaster. Most affected are the injured and those closest to the blasts. But even people with no physical injuries and those like Greeley who weren’t nearby can feel the emotional impact for weeks as they struggle to regain a sense of security. What’s not clear is who will go on to suffer lingering anxiety or depression, even post-traumatic stress disorder.

But how resilient people are can help determine how quickly they bounce back.

What’s resilience? It’s when people aren’t afraid to share their emotions so they don’t become overwhelmed — and when they try to look for a silver lining, like focusing on how many bystanders helped the wounded, rather than dwelling on gruesome memories.

Focusing on the horror, “that’s harder on our body and our mind,” said Dr. Catherine Mogil, co-director of the family trauma service at the University of California, Los Angeles. “People that tend to be able to make positive meaning out of tough situations are going to fare better.”

Typical reactions include: Difficulty sleeping or eating; sweats and stomachaches; anxiety or fear, especially in situations that remind people of the bombing like crowds. People may have a hard time focusing on work or other everyday activities. They may feel numb, get angry easily or cry often.

Seek help if those reactions are bad enough to impair function, or if they’re not getting better in about a month, said Priscilla Dass-Brailsford, a psychologist at Georgetown University Medical Center, who served on disaster mental health teams that counseled survivors of 9/11 in New York and Hurricane Katrina.

But for most people, “time is a great healer,” Dass-Brailsford said.

Specialists say only a small number of people are expected to be so severely affected that they develop PTSD, a disorder that can include flashbacks, debilitating anxiety, irritability and insomnia months after the trauma. Even among veterans of the Iraq and Afghanistan wars, the RAND Corp. estimated that just under 20 percent returned with symptoms of PTSD or major depression.

More at risk for lingering psychological effects are people who’ve previously been exposed to trauma, whether it’s on the battlefield or from a car crash or a hurricane.

During two stints in Iraq as a Marine, Eusebio Collazo of Humble, Texas, was gravely wounded and today runs to help him deal with PTSD. Running with a veterans group called Team Red, White & Blue, he was at mile 25 of the marathon when the bombs detonated — and adrenaline fueled his frantic race to find his wife, Karla, at the finish line. She was unharmed.

“I want to cry but I can’t,” Collazo said Thursday, saying it’s harder to handle explosions on the homefront than in a war zone. “There’s a lot of weird, different feelings going on.”

Dass-Brailsford, the disaster specialist, said part of coping involves taking care of yourself — turning off the scary TV coverage and reading a book, going out to a quiet dinner, anything that makes people feel better about themselves and even temporarily cuts the stress.

That’s especially true for parents who are trying to calm their children, added UCLA’s Mogil, because kids take their emotional cues from the adults around them. Younger children especially don’t need to see repeating footage of the blasts, because they may think it’s happening again.