Celine Dion says she's doing all she can to prove nothing can hold her back, even as she copes with Stiff-Person Syndrome ... 2 years on from when she was first diagnosed.

The icon admits she's upset she hasn't conquered the disease yet -- but, as she provided a rare update about her health to Vogue France, she insisted she was doing everything in her power to push forward in hopes science will eventually find a cure.

Celine acknowledges she's had serious moments of doubt, saying ... "I have to learn to live with it now and stop questioning myself. At the beginning I would ask myself: why me? How did this happen? What have I done? Is this my fault?"

She goes on, "The way I see it, I have two choices. Either I train like an athlete and work super hard, or I switch off and it's over, I stay at home, listen to my songs, stand in front of my mirror and sing to myself."

Celine explains she chose to work on her body and soul from head to toe ... pouring her all into rigorous athletic, physical and vocal therapy sessions 5 days a week to aid her recovery.

The legend's taking things one day at a time, but she's got her sights set on some big goals ... such as seeing the Eiffel Tower again and hitting the road for another tour.

Celine empoweringly added, "There's one thing that will never stop, and that's the will. It's the passion. It's the dream. It's the determination."

The "My Heart Will Go On" singer was diagnosed with SPS in 2022, and her sister previously revealed the autoimmune disorder, at times, leaves Celine completely immobilized.