In the Vietnam War, Bob Walker had been a helicopter mechanic, and he’d watched as his best friend was decapitated by an incoming helicopter’s propeller blade. Ever since then the 69-year-old Paradise, CA vet has struggled with post-traumatic stress disorder — a psychological condition that afflicts 7–8 percent of the population. It hits people who have been exposed to highly stressful situations in which their “fight or flight” response has been activated. Rape survivors. War veterans. Policemen.

People with PTSD can be highly irritable and suffer from insomnia, nightmares, and the inability to sustain deep relationships. Or, like Walker, they can walk through life feeling eternally numb. “Over the years, I tried everything from prescription drugs to biofeedback,” says Walker. “But nothing really worked. I knew something just wasn’t right.”