BOSTON -- It's been a tough four years for Ted Johnson since the linebacker retired from the Patriots.

In a rare interview with NewsCenter 5’s Liz Brunner, Johnson revealed how he battled addiction and serious health issues that, at times, left him unable to function.

"I've filled my quota on bad days," said Johnson.

During the past two to three years, Johnson said there were stretches when he spent 15 to 20 days in bed, losing touch with his friends, becoming unreliable.

"All my relationships suffered,” Johnson said. “I was not there for my kids. That's not really who I am."

Johnson and his doctors blame his depression, sleep disorder and mental fatigue on the countless concussions he suffered while playing football in college and 10-years in the NFL.

Johnson believes he has easily had 50, if not 100 concussions during his playing days, getting two a week, sometimes two during a single game.

Like most people, Johnson's understanding of a concussion is when a person is motionless on the ground, but has since learned that when you're hit, and then stumble, your balance and vision are off, anything that alters your normal brain function, that is a concussion.

"Sometimes I was the signal caller, and sometimes I couldn't see the defensive coordinator signal in plays and I'd have to ask another linebacker to call it because I couldn't see it. I would just sit there, and go, I hope my vision comes back before the start of the next play or I might get knocked on my can," he said.

“No one talked about what the long term effects were for concussions. I'd go into a game, I know I've torn biceps, both shoulders, I've ripped up a broken foot, I know I could injure myself that way, I didn't know what potentially I was doing to my brain getting these repeated concussions."

Even Johnson's doctors told him he'd reached new research territory and that they didn't know how to treat him. Exciting if you're in the medical profession, but a bit alarming if you're the patient, he told Brunner.

Doctors have a name for the damage that alters athletes’ brains; chronic traumatic encephalopathy, or CTE.

At the Boston University Brain Bank at the Bedford V.A., scientists are trying to unlock not only the mysteries of degenerative conditions like Alzheimer's and Parkinson's diseases, but also traumatic brain injuries of athletes.

Dr. Ann McKee, director of the Brain Bank, said in the football players’ brains they have studied, they are seeing clearly the exact abnormalities and damage that occurs from repeated concussions.

Johnson, along with about 50 other athletes, has agreed to donate their brains to science.

He said he and other former players want to do their part to figure this out.

But Johnson also said it has been difficult for him to watch some of his former football colleagues lose their jobs, become depressed, suffer failed marriages, or lose their life savings.

The pain and delirium of Johnson's concussion led to an addiction to amphetamines. Johnson said he is now completely "clean" and has stopped the addictive behavior and self-destructive behavior that plagued him the past few years.

He's also gotten back in shape, and says his friends tell him he's like the "old" Ted.

"That makes me feel good because I liked the old Ted. He's not a bad guy!"

Now Johnson is trying a new profession, teaching at Suffolk University and sharing his life lessons, something he says he loves doing.

Johnson loved football because it gave him an identity and a sense of purpose and feels that teaching at Suffolk is giving him that same feeling.

"In football," said Johnson, "if I could help entertain people for a few hours on Sunday, that made me feel good. When I get a response from students saying thanks for this, and we appreciate that, it's kind of the same feeling. I'm fortunate to have this opportunity."