CHICAGO —Corey Gibson’sright leg bounces when he sits. At 29 he sleeps fitfully, with an AR-15 semi-automatic rifle mounted above his bed. “”That’s my sense of security,”” he says.

Laurie Emmer, a 47-year-old mother of four, shuns crowds and strangers. She always sits facing the restaurant door when she goes out to eat and, before sitting down, makes sure to identify the quickest route out.

AndEric Johnson, 62, who revisits Vietnam nearly every night in his head, escapes the demons who rob him of sleep by patrolling the streets of his South Side neighborhood with his yellow Labrador retriever, Che.

The veterans come from different generations and different wars, yet they share a common and increasingly costly wartime affliction — post-traumatic stress disorder and other forms of psychological damage. Last year, mental illnesses accounted for 35 percent of the $22 billion spent on disability payments to veterans who served in the Vietnam, Persian Gulf and “”global war on terror”” eras, according to a Chicago Tribune analysis.

Compensating veterans with psychological scars has helped fuel a 76 percent surge in service-related disability costs since 2003, the Tribune found, burdening an already overwhelmed system and underscoring the reality that the biggest costs of war are not often immediate or visible.

Studies suggest costs will continue to soar. The percentage of military evacuations from Iraq and Afghanistan that were attributed to mental disorders has increased sharply in the last four years, a recent Defense Department study shows. Another survey of about 100,000 Afghanistan and Iraq veterans found that 31 percent had been diagnosed with mental health or psychosocial problems.

“”When you look at the epidemic of PTSD, you see the future,”” said Harvard University’sLinda Bilmes, co-author of the 2008 book “”The Three Trillion Dollar War: The True Cost of the Iraq Conflict.””

The Tribune’s analysis of claim records from the Department of Veterans Affairs found that vets’ psychological wounds are by far the most expensive type of disability. Compensating wartime veterans since Vietnam for PTSD and other mental conditions is four to five times costlier than the average for all disability categories, the Tribune found. Victims of PTSD also are more likely to suffer other serious and costly health problems than other disabled veterans. In short, they are sicker.

Gibson, Emmer and Johnson represent veterans at different stages of an evolving psychological struggle.

Johnson is a reminder that psychological damage can consume an adult life — in his case, 40 years. Johnson left South Vietnam in 1970, returning to Chicago after a year of tracking and killing the enemy in the jungle. He says he was ill-prepared for an abrupt transition to civilian life.

“”I felt stripped naked without a gun,”” said the burly, dreadlocked Johnson, who after his return would wear twin shoulder holsters carrying .45 automatics. When Johnson showered, he always took a gun, sealed in a plastic bag. He slept with a gun under his pillow. His first wife, Cookie, knew not to shake him awake or touch his feet.

For years he couldn’t acknowledge he had a problem, but in 1979 Johnson was diagnosed with PTSD.

The VA spent an estimated $5.6 billion last year compensating Vietnam veterans like Johnson for mental disorders, according to the Tribune analysis. That’s $4 of every $10 paid to disabled veterans from that war.

Johnson also reflects the reality that compensation payments to Vietnam veterans with psychological damage are, on average, 134 percent higher than payments to other disabled Vietnam vets. Johnson receives compensation for diabetes, high blood pressure, an intestinal disorder and a back injury sustained during a helicopter crash in Vietnam, in addition to PTSD.

PTSD has changed Johnson, a guarded man who is slow to trust strangers and rarely socializes. He ignores holidays and birthdays (including his own) and avoids family functions. The night terrors of Vietnam have receded but not gone away. Johnson still returns to Vietnam nearly every night.

Johnson’s second wife, Erma, has learned to recognize and deal with the enemy in his dreams. “”She’ll wake me up and say, ‘Don’t go — I got him,’ “” he said.

A retired postal worker who worked through his injuries, Johnson said he does not drink or take drugs, beyond pain relievers for his back and legs and medications to treat his diabetes.

“”Mentally, I’m a survivor,”” he said with a smile. “”I’m more fortunate than the average veteran because I’ve figured a few things out.””

Gibson is today where Johnson was in 1970. Volatile and solitary, Gibson tallies his losses after his tour of duty in Iraq — his fiance; three jobs from which he was fired; an active, engaging life that seems forever lost.

Gibson is part of a generation of younger vets whose problems are only starting to emerge. Last year, veterans of the war-on-terror era received $329 million in disability payments related to mental disorders, or 34 percent of the money paid to all disabled vets from the same era.

A paramedic from Terre Haute, Ind., Gibson signed up in 1999 for a five-year stint with the Army’s 555th Forward Surgical Team, whose job was to penetrate deep into the battlefield and provide emergency treatment for wounded soldiers advancing to the front. He entered Iraq in March 2003.

Gibson chooses not to dwell on what happened in Iraq, other than brief mentions of mortar attacks, taking prisoners and being blown from a truck during an attack on the way to Baghdad.

When he returned home in 2004, “”My fiance knew right away. ‘You’ve changed, you’re different,’ she kept saying,”” he said. There were night terrors and flashbacks. He became hypersensitive to perceived slights. “”It doesn’t help that I’m a male nurse,”” he said.

Gibson sleeps little and spends a lot of time alone, walking the neighborhood with his dog, Gibby. One night, while his fiance slept with her head resting on his chest, Gibson had a terrible nightmare and curled his body, putting her in a powerful headlock. She pounded on his chest to wake him up. Soon after, she left him, Gibson said.

He has been diagnosed with PTSD but also complains of other troubles, such as dizziness, a loss of long-term memory and back pain, which he says stems from his being thrown from the truck. After returning in 2004, he often slept less than an hour a night until he bought and mounted the rifle above his bed. “”My sleep went from 45 minutes a night to about two hours,”” he said. He calls the gun “”an extension of my arm.””

Gibson, who receives compensation for PTSD, recently filed a claim with the VA for traumatic brain injury. He spends most of his time at home, on his computer or watching videos. The shades are drawn.

Emmer, a retired Army sergeant, is among about a quarter-million women who have served in the wars in Afghanistan and Iraq, according to the Department of Defense. But the number that speaks to Emmer’s life-changing experiences is $50 million, the amount spent last year by the VA to compensate all female veterans from the war-on-terror era for psychological damage, according to the Tribune’s analysis.

A medic in the Army’s 82nd Airborne Division, Emmer waited 20 years to get an overseas combat assignment. Within a couple months of arriving in Afghanistan, her career as a skilled medic began to unravel. Emmer reported being raped by a coalition officer in Kandahar Province in the spring of 2003. In a separate incident, she injured her head falling off a military vehicle.

Today, the combination of PTSD and traumatic brain injury, or TBI, has enveloped Emmer in a light fog marked by physical imbalance, disorientation, anxiety and a round-the-clock headache. As a result of her injuries, Emmer is at a higher risk of stroke and early-onset Alzheimer’s disease. The ultimate cost of her maladies is unknown.

A pleasant woman with a boyish smile, Emmer appears on her front porch nearly every morning to plant the American flag and reappears to remove it at sundown. There is little physical evidence to suggest she is a severely wounded veteran.

But these days, when Emmer leaves the house, she writes down where she is going and why.

“”Unless you lose a limb, I don’t think other injuries resonate with the public,”” Emmer said in the living room of her Civil-War era home in rural Sycamore, Ill. “”Relatives wonder if we’re just making this stuff up, to get free money.””

She still longs to jump out of airplanes, which she did about 60 times during her 23-year military career with the 82nd. But that won’t happen. Emmer said she wants to go back to college and get a degree in history, so she can be a substitute teacher. But her doctor has advised against it, saying college might be too stressful.

Emmer, who has two children enlisted in the military, is determined to regain much of her old self. She finds support in other veterans “”on the roller coaster”” who are working toward the same goal. “”They want the old normal back,”” she said.