>>> BACK NOW ON "GMA" WITH NEWS OVERNIGHT FROM CELINE DION. THE MUSIC POWERHOUSE WHO HAS BEEN ABSENT FROM THE STAGE AMID HEALTH CONCERNS HAS NOW REVEALED THAT A BRAND-NEW EMOTIONAL VIDEO THAT SHE HAS BERNIE SANDERS DIAGNOSED WITH A RARE NEUROLOGICAL CONDITION. AND, LARA, YOU HAVE THE DETAILS. >> THAT'S RIGHT. IN THAT INSTAGRAM POST THIS MORNING, CELINE ADMITS SHE'S BEEN DEALING WITH HEALTH PROBLEMS A LONG TIME AND FINALLY FIGURED OUT THE CAUSE, A RARE AUTOIMMUNE DISORDER WHICH AFFECTS HER ABILITY TO PERFORM. ♪ BUT IT'S ALL COMING BACK TO ME NOW ♪ >> Reporter: THIS MORNING, CELINE DION MAKING A STUNNING ADMISSION ABOUT HER HEALTH. >> AS YOU KNOW, I'VE ALWAYS BEEN AN OPEN BOOK AND I WASN'T READY TO SAY ANYTHING BEFORE, BUT I'M READY NOW. I'VE BEEN DEALING WITH PROBLEMS WITH MY HEALTH FOR A LONG TIME, AND IT'S BEEN REALLY DIFFICULT FOR ME TO FACE THESE CHALLENGES AND TO TALK ABOUT EVERYTHING THAT I'VE BEEN GOING THROUGH. ♪ ALL BY MYSELF ♪ >> Reporter: THE SUPERSTAR POSTPONING HER 2023 TOUR AFTER BEING DIAGNOSED WITH A RARE NEUROLOGICAL DISORDER CALLED STIFF PERSON SYNDROME. >> WE NOW KNOW THIS IS WHAT'S BEEN CAUSING ALL OF THE SPASMS THAT I'VE BEEN HAVING. UNFORTUNATELY, THESE SPASMS AFFECT EVERY ASPECT OF MY DAILY LIFE, SOMETIMES CAUSING DIFFICULTIES WHEN I WALK AND NOT ALLOWING ME TO USE MY VOCAL CHORDS TO SING THE WAY I'M USED TO. IT HURTS ME TO TELL YOU TODAY. THIS MEANS I WON'T BE READY TO RESTART MY TOUR IN EUROPE IN FEBRUARY. ♪ THE POWER OF LOVE ♪ >> Reporter: IT WAS JUST THIS PAST OCTOBER WHEN CELINE WAS FORCED TO CANCEL THE REMAINING DATES OF HER NORTH AMERICAN TOUR CITING A HEALTH ISSUE. ♪ AND IN 2021 THE CANADIAN DIVA CANCELING A RETURN TO HER LAS VEGAS RESIDENCY AFTER SEVERE AND PERSISTENT MUSCLE SPASMS PREINVENTORIED HER FROM PERFORMING. ♪ MY HEART WILL GO ON ♪ >> Reporter: CELINE CLOSING HER HEARTFELT MESSAGE OUT WITH A GOOD-BYE FOR NOW TO THE STAGE. >> ALL I KNOW IS SINGING. IT'S WHAT I'VE DONE ALL MY LIFE, AND IT'S WHAT I LOVE TO DO THE MOST. I MISS YOU SO MUCH. I MISS SEEING ALL OF YOU, BEING ON THE STAGE. >> A REALLY HEARTBREAKING MESSAGE THERE. THE LIFE EXPECTANCY FOR A PERSON WITH STIFF MUSCLE SYNDROME IS 6 TO 28 YEARS FROM THE ONSET OF THE DISEASE. THE PROGNOSIS VARIES DEPENDING ON THE PERSON'S SYMPTOMS. DOCTORS ARE NOT SURE WHAT CAUSES IT. I SPEAK FOR ALL OF US WHEN I SAY SHE IS A LIFETIME TALENT AND WE WISH HER ALL THE BEST. >> WE'LL HAVE JEN, DR. JEN ASHTON IN OUR NEXT HOUR TO DISCUSS MORE ABOUT HER CONDITION. BUT YOU SAW HER AT THE GARDEN. I HAVE SEEN HER IN VEGAS. SHE GIVES HER ALL. >> WHEN YOU HEAR HER