Wheeler, a former Army medic who served for two years, was stationed at Fort Hood in 2014 when a gunman opened fire. Three of Wheeler's fellow soldiers were killed and 12 were injured before the shooter turned the gun on himself.

"It was frightening," Wheeler, now 28, told 60 Minutes+ correspondent Laurie Segall, "It was traumatizing, in a way."

After Wheeler was discharged in 2015, he said he didn't open up to his parents right away, and only over time gave more details about what he said he'd experienced during the shooting. But he told Segall the parents he returned home to had become more paranoid as they started being influenced by conspiracy theories. And they began to doubt his account of what he'd endured that day.