The singer’s ankylosing spondylitis went undiagnosed for years, and he wants to help others avoid the same fate

After years of “debilitating” upper body pain, Dan Reynolds questioned whether he would ever feel better again. The Imagine Dragons frontman had ankylosing spondylitis, a chronic autoimmune disease causing pain through the spine, but neither he — nor the multitudes of doctors he saw over two years — knew it.

“I was at the lowest low,” Reynolds, 31, tells PEOPLE. “I was depressed, I was in pain, I was scared about the future, I thought that I was going to be bedridden, right after we had our first baby. I couldn’t get out of bed to hold her when she was crying in the night. I thought I was going to be a terrible father. I thought that I wouldn’t be able to perform.”

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And while he and his Imagine Dragons bandmates are megastars now, when Reynolds was at the height of his pain in 2008 they were still in search of a label and hoping to make it big.

“There was a full year where I was just in pain and going to doctor after doctor, and at the same time trying to put on shows and move around the stage,” he says. “I remember one show where I couldn’t even move.”

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Reynolds didn’t know if he had much of a future.

“I thought this was the end of my career,” he says. “I had been beaten down by this hidden disease. It was really debilitating and scary.”

But thankfully, Reynolds’ brother, who had recently been diagnosed with ankylosing spondylitis, or AS, after similar pain, suggested that he go see a rheumatologist, who determined that he had the same condition.

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With the help of his rheumatologist, Reynolds started changing his diet, workouts and began a treatment plan that immediately worked.

“That week I saw improvements,” he says. “Once you have a treatment plan it’s like night and day. Seeing a rheumatologist was life-changing for me.”

After a few years of trial and error, Reynolds is in a place where he has occasional pain, but he’s “able to do all the things that I love and live a healthy, strong life.” And he wants to help others by raising awareness of AS — a common condition, with more than 200,000 cases in the U.S. each year, but one that people and doctors often aren’t aware of.

To make AS “mainstream,” Reynolds is partnering with the Novartis Pharmaceuticals Corporation on their Monster Pain in the AS campaign.

“I want people to get started on this process and go to website, where they can take a three-minute quiz to see if they have AS and hopefully get started on the process that took me years to figure out,” he says. “My diagnosis has been life-changing in every possible way just because I saw a rheumatologist. That’s why those three minutes of taking the quiz are so important.”

Image zoom Dan Reynolds for the Monster Pain in the AS campaign Novartis Pharmaceuticals Corporation

Along with bringing awareness to AS, it’s important to Reynolds to speak openly about his condition.

“I think we live in the age of Instagram, where everybody’s putting up their best moments and taking pictures in the best light with the best filter,” he says. “But what I think is really important is to talk about our insecurities and our pain, the things that are hard. It helps other people feel less alone. Everyone is struggling with something. If we’re all putting out a false narrative of perfection the world seems a lot more lonely.”

Reynolds says that sharing his story on social media has helped him.