The question, tossed at Michael J. Fox from off-camera by the accomplished documentarian Davis Guggenheim, gets at a truth so blunt and self-evident that it doesn’t require an answer.

“Why do you want to tell this story right now?“

And Fox considers not answering it. He has Parkinson’s, and in “Still: A Michael J. Fox Movie,” we’ve already seen how far the debilitating “incurable” illness has progressed. If he doesn’t sit for interviews and read from his autobiography and “host” this film about him now, he might never be able to.

But he doesn’t want that sort of “sad” and “pity” filled biography about an illness that “crushed him.”

“That’d be BORING” he blurts. Think of him as a “cockroach,” he insists. “You can’t KILL a cockroach.”

“Still” is exactly the sort of documentary you’d expect from Fox, whose control of its tone, if not its brisk pace, he seems to have exercised control over. It’s a brief summation of his early life and career, a breezy account of his burning-the-candle-at-both-ends peak, filming TV’s “Family Ties” during the day, knocking out “Back to the Future” and the other movies that made him after hours or when the TV show was on hiatus.

He takes us back to that first day — in a Miami hotel in 1990 — when he woke up, hungover and yet realizing something was wrong with his “auto-animated pinky” suddenly having developed a mind of its own. And he’s sanguine about the dream life he lived before that morning and the diagnosis that followed, and the “cosmic price” or even “karma” he can attach to the disease that arbitrarily and progressively took over his life and all but ended his career.

Fox lets himself get choked-up over his Canadian armed forces veteran turned police dispatcher dad, who didn’t discourage his quite-small-for-his-age son from getting into acting, and who “surprised me” by personally driving him to Hollywood to start the stretch of auditions that would lead — eventually — to his first big break, then the bigger ones that followed.

He puts the sweetest celebratory spin on meeting and insult-flirting with his future wife, Tracy Pollan, on the “Family Ties” set. She wasn’t impressed with his stardom and was nobody’s idea of a fair weather “Hollywood wife” when the chips were down.

“How’s Tracy?” his physical therapist asks at a session.

“Married to me…still.”

Parkinson’s may play havoc with an actor’s comic timing. Fox’s was and is so good it overwhelms his condition, which has him dealing with a succession of tumbles, bruises and broken bones over the course of filming “Still.”

We see him take such a fall while walking with a bodyguard-aid as he’s leaving their New York luxury flat. Captured in long-shot, a concerned passersby instinctively reaches down to help. “I’m OK,” he insists, and she recognizes him.

“Very nice to meet you,” she says.

“You knocked me off my feet!” he jokes, and charms her socks off.

“Still” has moments like that, interviews and therapy sessions and a running account of Fox’s career and Hollywood celebrity, many of them recollected from his memoirs. We glimpse him at his “Ferrari, Range Rover and Jeep Cherokee” peak, and on the night he came clean with his fans on a TV chat show about the hidden, heavily-medicated illness that had slowed him down, muzzled his performances and which at least partically explains the tide-turning bombs (sampled in “Siskel & Ebert” clips) that brought his film career to an end.

“Still” was what he could never be as a child, recalling the time he grabbed cash and dashed through the back door to the local candy store while his parents were distracted. The store owner called to alert them he was there with a wad of cash and a taste for sweets. They’d best come fetch him. Fox was two.

These days, thanks to his illness, being “Still” is even more impossible.

His small stature, we’re told, informed his early career. He could play “older, smarter” kids into his 20s, something his first Canadian collaborators tipped him about, “cute and elfin,” traits which sent him to Hollywood.

Fox takes pleasure in reminding the world how producer Gary David Goldberg and NBC programming chief Brandon Tartikoff resisted casting him in “Family Ties,” the “he’ll never be on a lunchbox” limitations that Tartikoff famously scoffed.

Then we see him improvise/invent his character’s middle initial — “Alex P. Keaton” — in a moment in the “Family Ties” pilot, hitting the letter perfectly, instinctively knowing that “Pee” coming out of a short, sweater-vested conservative was funny. Tartikoff got an autographed lunchbox from Fox for Christmas.

“I feel FOUR feet tall!” Fox crowed, upon winning an Emmy for the work.

That on-screen cockiness, delivered when the actor was down to his last Roosevelt dime, has informed our image of Michael J. Fox ever since and spills over into his and his foundation’s battle against his illness.

Fans, people who grew up with him, took the Parkinson’s news hard. But his pugnacious Canadian Cagney demeanor allowed us hope, and every Parkinson’s breatkthrough underwritten by the Michael J. Fox Foundation seems to validate that hope.

They may not name the illness after him, which could finish him before his time. But when the “tough son of a bitch” underwrites the research that ends Parkinson’s, you can be damned sure his name’ll be on the cure.

Rating: R, profanity

Cast: Michael J. Fox, Tracy Pollan, and the voice of Davis Guggenheim

Credits: Directed by Davis Guggenheim. An Apple TV+ (May 12) release.

Running time: 1:35