The 71-year-old told Roberts he could no longer hide his health struggles and that he is on a "whole host" of medication for pain.
Osbourne said it began after a fall last year which required surgery.
"It's been terribly challenging for us all," Osbourne told Roberts. "I did my last show New Year's Eve at The Forum. Then I had a bad fall. I had to have surgery on my neck, which screwed all my nerves."
"It's PRKN 2," said his wife, Sharon, in the GMA interview. "There's so many different types of Parkinson's; it's not a death sentence by any stretch of the imagination, but it does affect certain nerves in your body. And it's -- it's like you have a good day, a good day, and then a really bad day."
Osbourne postponed a world tour last year and spent much of the year in seclusion.