"Like the click of a gun, that might be a twig or something," Sergeant Roy Parks said.
Everyday life sounds like war to Parks. It is a war going on in his mind.
"Loved the Fourth of July," he said. "Now I can't stand it because of the whistling, the booms."
Parks has post traumatic stress disorder, or PTSD. It's an emotional illness that develops after a person goes through a traumatic event.
"I'll wake up and fall on the floor," Parks said. "I'll wake up and duck down."
Parks sought treatment early and has been in therapy four years. He says he thought it would get better once it got home, but it didn't.
According to the Department of Defense, up to 30 percent of veterans from Iraq and Afghanistan will suffer from PTSD.
But the VA only tracks service members who go to them for treatments. So experts believe the number of veterans walking around with PTSD is actually a lot higher.
Dr. Eva Usadi is a trauma therapist who specializes in PTSD.
"I think what tends to happen is that families let it go for a long time," she said.
Instead, families should watch for the following signs:
With early detection and therapy, Dr. Usadi says PTSD is manageable.
"It's sort of like when a person breaks a leg or another bone, and it heals, it's actually stronger than it was before," she said.
Parks is optimistic he will get better. And he knows it could get worse.
"I do go to the VA, and I see guys that have been out from Vietnam for 20 years, 30 years, and they still got their quirks," he said. "And I look, I'm like, is that going to be me?"