The 42-year-old actor, who worked as a full-time WWE wrestler until 2004, told The Hollywood Reporter in a new interview that he first experienced depression as a college football player at the University of Miami.
He sustained several injuries and dropped out of school.
"I didn't know why I didn't want to do anything. I had never experienced anything like that," he said.
It wasn't until his coach called and encouraged him to return that he recovered.
"He says, 'Get your ass in a car and come back right now,' " Johnson recalled. "He was so embarrassed and pissed. It's one thing when you go through an injury and depression. It's another when you walk away and say, 'F*** it.'"
Johnson also remembers feeling devastated when he didn't make the NFL draft. He was signed by Canadian Football League's Calgary Stampeders, but was eventually cut.
"The dreams I had, they're dashed," he said. "There is no more football. My relationship was crushed. That was my absolute worst time."
His bout occurred after his 2008 divorce from Dany Garcia, his wife of 10 years, with whom he had a daughter.
"Once I manned up and became accountable for the mess I was in, that's when it hit me," he said. "What kind of a dad does this make me? What kind of a man will I now become? Failing at marriage and as a husband was a heavy thing, and divorce had that special way of knocking me on my ass."
These days, though, Johnson said he's happily living with his 29-year-old girlfriend, Lauren Hashian, and is set to star in Hercules, which opens July 25.