The Piano Man crooner, 76, worried fans in May when it was announced he had been diagnosed with normal pressure hydrocephalus (NPH), a rare but treatable condition that affects the brain and can impair hearing, vision and balance.
In an update about his condition, he has now urged fans not to worry about him.
"I know a lot of people are worried about me and my health, but I'm okay," Joel told People.
"What I have is something very few people know about, including me, no matter how much you try to research it. I'm doing my best to work with it and to recover from it."
The singer's diagnosis was first shared publicly in a statement through his team. He said balance issues were his earliest and most persistent symptom.
"It was like being on a boat all the time," he told People.
"It was scary, but I'm okay. I just wanted to let people know, don't worry about me being deathly ill or anything."
Following his diagnosis, Joel cancelled all scheduled performances, with his representatives confirming his condition had been exacerbated by recent concerts.
"Billy is undergoing specific physical therapy and has been advised to refrain from performing during this recovery period," a statement at the time said.
"Billy is thankful for the excellent care he is receiving from fans during this time and looks forward to the day when he can once again take the stage."
The singer added to fans: "I'm sincerely sorry to disappoint our audience, and thank you for understanding."
Joel's wife, Alexis Joel, 42, shared a message on Instagram alongside a family photo including their daughters, Della, nine, and seven-year-old Remy.
"Thank you for the outpouring of love and support. We are so grateful for the wonderful care and swift diagnosis we received," she wrote.
"Bill is beloved by so many, and to us, he is a father and husband who is at the centre of our world. We are hopeful for his recovery. We look forward to seeing you all in the future."
Joel's eldest daughter, 39-year-old Alexa Ray Joel - his child with ex-wife Christie Brinkley - also expressed support on social media.
"We love you and we got you, Pop!" she wrote.
"My Dad is the strongest and most resilient man I've ever known … and he's entirely committed to making a full recovery with ongoing physical-therapy treatments as he continues to regain his strength."
Joel's health update comes amid renewed interest in his life and work due to the HBO documentary Billy Joel: And So It Goes.
The two-part feature, which premiered last week, features in-depth interviews with Joel and explores key moments of his six-decade career.
Part two is set to stream on Saturday AEST.
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