For veterans, the puff of diesel exhaust from a passing bus or a song on the radio can bring them back to their military vehicle in the battlefield.
For some, it is a memory that will fade in and out. For others, it is more severe and called post-traumatic stress disorder, or PTSD.
Not everyone who goes to war returns with PTSD, said John Mundt, a clinical psychologist at the Jesse Brown VA Medical Center in Chicago for 20 years.
"PTSD is just one possible response to trauma," Mundt said.
It is not a disorder of bad memories.
"It's a disorder about reliving," he said. "It's like they eat a bad meal that keeps coming up again and again."
The VA cannot force veterans to seek treatment. "They have to come in when they're ready," Mundt said.
The optimal time to address mental issues is immediately after the trauma happens.
Some National Guard units are requiring that 30-45 days after a unit returns from war, the guardsmen must regroup and meet with job, school and mental health counselors to learn about benefits, Mundt said.
One local option is through the Veterans Life Changing Services, 501 W. Ridge Road, in Gary, which offers assistance to veterans transitioning back to civilian life.
In uniform, veterans are respected as heroes. But they are often stigmatized, especially if they need accommodations for their mental health, said Bessie Hitchcock, director of operations at Veterans Life Changing Services (VLCS).
Many are fighting an invisible war. Unlike an enemy in battle, veterans can't see the mental anguish they're up against, often turning to drugs and alcohol to cope, she said.
"They do what they think they have to do to survive and exist," Hitchcock said.
Her husband served as a marine sergeant in the Vietnam War.
"I see what the war has done to him," she said. "He is still dealing with that invisible war."
At their home, all the lights have to be on at night, and every door with a lock needs to be locked. When he first came home from Vietnam, the kicking and flailing in his sleep would awaken Hitchcock, but her husband had no memory of it.
"I deal with it, I live with it," Hitchcock said.
She wants to form a support group for veterans' spouses. Those interested in joining can call her at (219) 979-0900.
On top of the war experiences that can lead to PTSD, there is the threat of military sexual trauma, called MST. It is so prevalent that each VA in the country must have an MST coordinator to triage the cases, Mundt said.
MST, which includes sexual assault and threatened assault in the context of severe, persistent hazing and harassment, is not a condition, but a person could have PTSD from a sexual trauma, he said.
Mundt said that, in his particular high-acuity crisis-focused VA mental health program, three of five female referrals have a history of sexual trauma in the military. Overall, approximately one in four of all female veterans has experienced MST.
One of Mundt's patients was sexually assaulted by a commanding officer who wore a distinct cologne. The smell of any strong cologne triggered that memory.
Another patient was being treated for PTSD. She witnessed a friend's vehicle go up in flames, and she tried to put out the fire. In their talks, she disclosed she was a victim of date rape and also had been gang raped by soldiers in her unit.
Sexual assault in the military is further complicated by the betrayal involved. A victim may later need to put her life in her attacker's hands.