Johnny Manziel Diagnosed Bipolar, 'Self-Medicated with Alcohol'

Johnny Manziel says he's been battling bipolar disorder and depression for years -- and had used alcohol as a way to "self-medicate" ... but claims he's sought professional help to work through it.

"I am taking medication for bipolar, and I am working to try to make sure I don’t fall back into any type of depression," Johnny told "Good Morning America" ... "because I know where that leads me and I know how slippery a slope that is for me."

Manziel says he was diagnosed as bipolar about a year ago -- around the same time he decided to start changing his life and begin his pro football comeback.

"I am watching all the other guys doing what I want to be doing, and I am sitting on a couch being a loser."

"The goal of this comeback is to get back to the NFL, ultimately."

As for his battle with booze -- Manziel explained, "I was self-medicating with alcohol. That’s what I thought would make me happy and get out of that depression."

"When I would wake up the next day after a night like that, going on a trip like that, and you wake up the next day and that is all gone, that liquid courage, or that liquid ... sense of euphoria that is over you, is all gone."

"You are left staring at the ceiling by yourself, and in that depression and back in that hole, that dark hole of sitting in a room by yourself, super depressed, thinking about all the mistakes you made in your life."

"What did that get me? Where did that get me except out of the NFL? Where did that get me? Disgraced?"

Johnny says the support from his family and his fiancee, Bre Tiesi, have been key to getting his life back together.