In an upcoming episode of Running Wild With Bear Grylls on National Geographic, Ashton Kutcher says he was incapacitated by an autoimmune disorder called vasculitis two years ago. “I had this weird, super-rare form of vasculitis that, like, knocked out my vision. It knocked out my hearing. It knocked out, like, all my equilibrium,†says Kutcher in the clip, obtained exclusively by Access Hollywood. Vasculitis is marked by an inflammation of the blood vessels. “It took me like a year to, like, build it all back up,†added Kutcher. “You don’t really appreciate it until it’s gone, until you go, I don’t know if I’m ever going to be able 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.†Luckily, the actor recovered enough to not only brave the Costa Rican jungles with Grylls but also act in the upcoming Netflix sequel to That ’70s Show, That ’90s Show. The Running Wild episode will premiere August 8 on National Geographic and stream on Disney+ on August 10.