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Actor Ashton Kutcher opened up about a health scare that left him lucky to be alive.

On an upcoming appearance of National Geographic’s Running Wild With Bear Grylls, the actor revealed he suffered a rare and intense form of vasculitis.

 “Two years ago, I had this weird, super rare form of vasculitis. It knocked out my vision. It knocked out my hearing. It knocked out all my equilibrium. It took me like a year to build it all back up,” he tells Gyrlls in the episode, per Access Hollywood.

The star of “That 70’s Show show says, “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,” he said. “I’m lucky to be alive.”

According to The Mayo Clinic, “Vasculitis involves inflammation of the blood vessels. The inflammation can cause the walls of the blood vessels to thicken, which reduces the width of the passageway through the vessel. If blood flow is restricted, it can result in organ and tissue damage.”

Ashton’s episode of Running Wild will air on Monday, August 8.