(WJW) — Actor Ashton Kutcher recently revealed he was diagnosed with vasculitis, an autoimmune disorder that took away his ability to walk, see and hear.

The 44-year-old actor opened up about the health scare in an episode of “Running Wild With Bear Grylls: The Challenge,” a show in which celebrities undertake adventures with Grylls through the wilderness while learning and applying survival skills.

“Two years ago, I had this weird, super-rare form of vasculitis that knocked out my vision, it knocked out my hearing, it knocked out all my equilibrium,” Kutcher said during the episode, which aired Monday on the National Geographic channel.

Kutcher said it took nearly an entire year to get back to full strength, making clear he’s “lucky to be alive.”

“Don’t really appreciate it until it’s gone,” he told Grylls. “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 causes blood vessels to inflame, according to the Cleveland Clinic, and can lead to aneurysms, thinning of the blood vessels, or closing off of the blood vessels. The cause of the disorder is unknown, but experts say in most cases, something has caused an immune or allergic reaction in the walls of the blood vessels.

This isn’t the Iowa-born celebrity’s first time dealing with major health issues. He also notably ended up in the hospital while filming the Steve Jobs biopic “Jobs” after trying to follow the Apple co-founder’s diet. Drinking mostly carrot juice reportedly gave Kutcher pancreatitis, twice.

Kutcher is married to fellow “That ’70s Show” actor Mila Kunis, and the pair have two children.