The superstar singer has stiff-person syndrome, which affects "something like one in a million people," Dion, 54, said in an emotional video post Thursday to her verified Instagram account.
"While we're still learning about this rare condition, we now know this is what's been causing all of the spasms that I've been having," she said. "Unfortunately, these spasms affect every aspect of my daily life, sometimes causing difficulties when I walk and not allowing me to use my vocal cords to sing the way I'm used to."
Stiff-person syndrome is "a rare, progressive syndrome that affects the nervous system, specifically the brain and spinal cord," according to the National Institute of Neurological Disorders and Stroke.
"Symptoms may include extreme muscle stiffness, rigidity and painful spasms in the trunk and limbs, severely impairing mobility," the institute says. "Spasms can generate enough force to fracture bone."
Specific treatments "will improve the symptoms ... but will not cure the disorder," it says.
Dion has struggled with her health for a while, she said, adding she has a great team of medical professionals and her children's support.
"I'm working hard with my sports medicine therapist every day to build back my strength and my ability to perform again," she said. "But I have to admit it's been a struggle."
The Grammy winner said singing is all she knows -- and what she loves.
"I miss you so much," she said. "I miss seeing all of you, being on the stage, performing for you. I always give 100% when I do my shows, but my condition is not allowing me to give you that right now."
Dion has "hope that I'm on the road to recovery," she said. "This is my focus."
She thanked her followers for their "encouraging wishes of love and support by social media."
"This means a lot to me," Dion concluded her message tearfully. "Take care of yourselves. Be well. I love you guys so much, and I really hope I can see you again real soon."
Dion's spring 2023 shows will be rescheduled to 2024, and eight summer 2023 will be canceled, the post said.
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