Michael J. Fox has inspired millions with his endless optimism after disclosing his Parkinson’s disease diagnosis to the public in 1998. 

But the actor, 59, also has some dark days where he feels overwhelmed and hopeless about his health prognosis. Fox details his internal struggles in his upcoming fourth memoir, "No Time Like the Future."

The "Back to the Future" star recalled to People magazine how one night, in particular, a few years ago, he "questioned everything." Fox fell in his New York City apartment and broke his arm. 

“That was definitely my darkest moment,” he said “I just snapped. I was leaning against the wall in my kitchen, waiting for the ambulance to come, and I felt like, ‘This is as low as it gets for me.’ It was when I questioned everything. Like, 'I can't put a shiny face on this. There's no bright side to this, no upside. This is just all regret and pain.' "

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During that time, Fox was also recovering from spinal surgery he underwent in 2018. “I was heading for paralysis if I didn’t get it operated on,” he explained. 

Actor Michael J. Fox disclosed his Parkinson’s disease diagnosis to the public in 1998. 

Actor Michael J. Fox disclosed his Parkinson’s disease diagnosis to the public in 1998.  (Jim Spellman/WireImage)

The entertainer had a noncancerous tumor removed. It was "growing was constricting the [spinal] cord, so they had to be very careful in removing it so they wouldn’t do further damage,” Fox described. 

He added, “Parkinson’s, my back, my arm … it still didn’t add up to moving the needle on the misery index compared to what some people go through. “I thought, ‘How can I tell these people, “Chin up. Look at the bright side. Things are going to be great”?’"

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Fox said he had to recoup in bed and used the time to reflect. 

"Optimism is really rooted in gratitude," he said. "Optimism is sustainable when you keep coming back to gratitude, and what follows from that is acceptance. Accepting that this thing has happened, and you accept it for what it is. It doesn't mean that you can't endeavor to change. It doesn't mean you have to accept it as a punishment or a penance, but just put it in its proper place. Then see how much the rest of your life you have to thrive in, and then you can move on."

Tracy Pollan and Michael J. Fox married in 1988 and have four children together. 

Tracy Pollan and Michael J. Fox married in 1988 and have four children together.  (Nicholas Hunt/Getty Images for Tribeca Film Festival)

Fox continued, "My gratitude is deeper now, from having gotten through the darkest times."

The activist also emphasized that even though his life has changed since 1998, he is living it to the fullest. “My life now is quiet, and I’m actually having a really good time,” Fox gushed. “People don’t believe me, but I love life. I love being with my family."

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Fox married wife Tracy Pollan in 1988 and the couple shares son Sam, 31, twins Aquinnah and Schuyler, 25, and daughter Esmé, 19.