Celine Dion Can Only Be Herself

“I always envy people who smoke and drink and party and don’t sleep,” Celine Dion tells her physical therapist with an exaggerated sigh, midway through the new documentary “I Am: Celine Dion.” “Me, I have water and I sleep 12 hours.”

This monastic constraint has long been a core part of the Celine Dion legend. A professional singer since 12, she spent decades meticulously caring for her voice as though it were an endangered hothouse flower, committing to long stretches of vocal rest, complicated warm-up rituals and a lifestyle of exacting discipline — all so she could leap octaves and belt soaring notes with gobsmacking precision.

In a cruel twist of fate, though, even the ceaseless care Dion devoted to her voice could not preserve it. In 2022, she revealed in an emotional Instagram post that she has stiff person syndrome, a rare and incurable neurological disorder that causes painful muscle spasms and affects roughly one in a million people. After watching “I Am: Celine Dion,” a remarkably candid portrait directed by Irene Taylor on Amazon Prime Video, it is difficult to imagine a disease that would be more personally devastating to Dion, whose entire career has been one long exercise in control, sacrificing all for the ecstatic release of live performance.

Since her emergence as a Québécois child star with a precociously huge voice, something about Dion’s essential nature has remained constant, impervious to both changing trends and scathing critique. Whether power ballads were in fashion or not — and by and large, they were not — she sang them with the conviction of someone who’d never even heard the word “restraint.” “At her best,” wrote Elisabeth Vincentelli in a Times review of Dion’s most recent New York performance in February 2020, “Dion projects a sense of bigness — besides fairly simple graphics, the background videos in her show often showed cosmic images, as if they were the only thing measuring up on the Dion scale.” This bombastic approach gained her a worldwide fan base and a requisite backlash that she may have finally outpaced.

In 2007, the music critic Carl Wilson used Dion’s 1999 blockbuster album “Let’s Talk About Love” as the inspiration for an insightful, ultimately sympathetic book-length examination of musical taste, the assumption being that (at least 17 years ago) Dion’s name was a symbol for all things gauche, sincere and uncool. (The book’s subtitle? “A Journey to the End of Taste.”) “Schmaltz rots faster than other ingredients in the musical pantry,” Wilson wrote, “which may be why we doubt the possibility of a Celine Dion revival in 2027.”