Ozzy Osbourne didn't believe son Jack's MS diagnosis at first: 'He got misdiagnosed with MS in the '90s'

Reality TV star Jack Osbourne was away from home working, when he suddenly lost vision in his right eye. “Forty-eight hours later, I was about 90 percent blind in my central vision,” he shares with Yahoo Lifestyle.

Doctors ran “every single test imaginable,” including an MRI, he says. That MRI determined that he had lesions in his brain and spine — classic signs of multiple sclerosis. He was just 26 years old at the time.

Multiple sclerosis (MS) is an often debilitating disease that can cause symptoms like fatigue, difficulty walking, numbness or tingling, weakness, spasticity, pain and emotional changes, according to the National Multiple Sclerosis Society.

Jack, who shares three children with ex-wife Lisa Stelly, was diagnosed with the disease three weeks after his oldest daughter was born. “You’re on this high, like, ‘Yeah, I have this new baby,’” he says. “It was like getting punched out of nowhere.”

His father, rocker Ozzy Osbourne, was misdiagnosed with MS in the ’90s and tried to write off his son’s diagnosis at first, Jack shares. “My dad was very much of the mindset of like, ‘No, that’s wrong.’ His inkling is, it’s still the 1990s and they’re still not good at diagnosing it,” says Jack. And “my mom does not deal with bad news very well,” he adds.

Jack became an advocate to help spread awareness of the disease. He also started a website called You Don’t Know Jack About MS to help educate others about the condition and provide resources for others with MS.

He says that he’s struggled with depression as a result of his illness. According to the National Multiple Sclerosis Society, depression is one of the most common symptom of MS, and is more common among people with the disease than it is in the general population and among many people living with other chronic, disabling conditions.

“Depression has definitely been prevalent for me,” Jack says. “At least a couple nights a week, I’ll go to sleep thinking, ‘Ugh. I hope tomorrow is not one of those days.’”

Despite depression being so common among MS patients, Jack says, “The mental component is something that’s the least talked about.”

Osbourne also struggles with fatigue at times. “A bad day for me is like one o’clock in the afternoon, I’ve had eight hours of sleep, and I can’t get off my couch because I’m completely wiped,” he says. “I don’t like wasting a day. I feel like I have to be as active as possible.”

That’s why Osbourne now does CrossFit, rock climbing and surfing, and tries to work more than he has in the past on his paranormal investigation show Portals to Hell, which is on the Travel Channel.

A few years ago, Jack says he “made it my full-time job to get out in front of this as much as possible and to be as active as possible.” That seems to have helped him function better now, he says. “I’ve been able to live a very high-functioning life and most of my friends forget that I have [MS],” he says.

Jack is hopeful about the future and happy with what he’s achieved so far. “If it gets bad and I can’t go on, well, I can’t go on,” he says. “At least I’ve tried and had this experience. And hopefully I encourage people who have MS who think they can’t do something to get out there and do it.”

Read more from Yahoo Lifestyle:

• The MS symptom that’s the worst for this teen: ‘just loneliness’

• ‘I thought my life was over’: What it’s like to be diagnosed with a chronic illness at 19 years old

• How Meredith Vieira’s husband, Richard Cohen, realized he had MS: ‘I dropped a coffeepot for no reason’

Follow us on Instagram, Facebook, and Twitter for nonstop inspiration delivered fresh to your feed, every day.

Want daily lifestyle news delivered to your inbox? Sign up here for Yahoo Lifestyle’s newsletter.