Brett Favre is admitting he was initially terrified to learn of his Parkinson's diagnosis ... telling TMZ Sports he at first thought "it was the end of the world."

Favre got candid with us about his much-publicized health battle last week ... revealing that when docs told him he had the disease in January 2024 after having some troubles with his right hand, his initial thoughts were pessimistic ones.

He said he believed "the world was caving in on me" ... and he wondered out loud how this all happened.

"I'm healthy," he said. "I'm very active. I mean, it doesn't happen to me."

Favre, though, says now that it's been a year ... he's got a far different mindset.

"I'm trying to live in the present," he said, "and just make the most of what I've got."

The 55-year-old Hall of Famer pointed to his family, his friends and his "great support group" for reasons to remain positive. He also said the Parkinson's medication he's taking has managed his symptoms.

He did, however, reveal his mind does stray sometimes to what could possibly be on the horizon -- telling us, "There's always the fear of what happens next -- what's the next step?"

But, check out our chat with the former Green Bay Packer, it seems clear those thoughts are becoming fewer and farther between as his good days continue to mount.