The actor revealed his experience with vasculitis on Running Wild With Bear Grylls: The Challenge.

Ashton Kutcher knows a thing or two about challenges.

On a new episode of the survival series Running Wild With Bear Grylls: The Challenge, the That '70s Show star reveals that he came down with a rare autoimmune disorder a few years ago that left him temporarily deaf and blind and caused him to lose his sense of balance.

In a clip from the episode, which will air Monday night on National Geographic, host Bear Grylls asks, "I've never met any strong person who's had an easy road. Where does that strength come from with you?"

"Like two years ago, I had this weird, super rare form of vasculitis that like knocked out my vision, and knocked out my hearing, and knocked out all my equilibrium," Kutcher replies. "It took me like a year to build it all back up. You don't really appreciate it till it's gone, until you go, 'I don't know if I'm ever going to see again. I don't know if I'm ever going to be able to hear again. I don't know if I'm ever going to be able to walk again.'"

He adds that he's "lucky to be alive."

As harrowing as the experience sounds, it seems to have given Kutcher some unique perspective on overcoming adversity. "The minute you start seeing your obstacles as things that are made for you to give you what you need, then life starts to get fun, right?" he says. "You start surfing on top of your problems instead of living underneath them."

The current season of Running Wild: The Challenge has produced several intense moments, from Natalie Portman drinking water filtered through Gryll's underwear to Simu Liu resurrecting a maggot with the heat of his tongue. As for Kutcher, he'll also been seen in less spartan surroundings on the upcoming That '70s Show spin-off That '90s Show.

Watch the video above for more from Kutcher and Grylls.

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