Ashton Kutcher has spoken for the first time about his experience with a rare autoimmune disease that left him struggling to walk, see and hear.

Kutcher is starring in an upcoming episode of Running Wild with Bear Grylls: The Challenge, and Access Hollywood obtained an exclusive look at Kutcher’s appearance on the series, in which he discusses his battle with a rare form of vasculitis.

“Like 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.” It took him about a year to build each back up again,” he tells Grylls in the episode.

He says his case lasted for a year and became really traumatic, giving him a newfound appreciation for his physical health. “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’.”

Vasculitis is quite serious, and experiences range from fever and numbness or weakness in extremities through to debilitating issues in the body such as inflammation of the blood vessels and restriction of blood flow, which in turn can lead to organ and tissue damage.

Thankfully, Ashton has made a full recovery. But he explained to Grylls in the episode he feels “lucky to be alive” after his experience, and that it’s taught him to “start seeing your obstacles as things that are made for you, to give you what you need.”

Ashton Kutcher’s episode of running Wild with Bear Grylls: The Challenge airs Monday on National Geographic in the US.