In an upcoming episode of National Geographic’s “Running Wild with Bear Grylls: The Challenge,” the That ’70s Show star reveals that he developed a rare autoimmune disorder. “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,” he explained in the exclusive clip obtained by Access Hollywood. Kutcher—who is pretty private when it comes to his personal life—explained that it took about a year to rehabilitate each sense, adding that the incident really changed his perspective on health. “You don’t really appreciate it, until it’s gone,” he stated, adding, “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’.” He noted that he’s “lucky to be alive.” Kutcher also revealed that the scary incident helped him see every challenge as an opportunity to grow in life. “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? You start surfing on top of your problems instead of living underneath them,” he said. According to the MayoClinic, vasculitis is an inflammation of the blood vessels that reduces the passageway and can cause organ and tissue damage. There are many types of vasculitis, and though they can be life threatening, they are rare. There is currently no cure, but early diagnosis and treatment are beneficial. The episode of Running Wild will air on Monday, August 8, on National Geographic at 9 PM ET. More Pop culture:

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