The widow of actor Robin Williams has opened up about her late husband's battle with a rare neurologic disease in the final months of his life.

Susan Schneider Williams’ has penned an essay entitled 'The Terrorist Inside My Husband’s Brain', published in the medical journal Neurology. In her piece, she describes "the little-known but deadly Lewy body disease (LBD)", from which Williams suffered, and recounts the horrible symptoms he had to deal with in the last 10 months before his death in 2014. They include "constipation, urinary difficulty, heartburn, sleeplessness and insomnia, and a poor sense of smell—and lots of stress." She also reveals that Williams suffered from "paranoia, delusions, and looping". [caption id="attachment_313758" align="aligncenter" width="3000"]

Robin Williams speaks onstage during the 65th Annual Primetime Emmy Awards, September 2013 (Kevin Winter/Getty Images)

[/caption] She writes:

“My husband was trapped in the twisted architecture of his neurons, and no matter what I did I could not pull him out. Robin was losing his mind and he was aware of it. Can you imagine the pain he felt as he experienced himself disintegrating? And not from something he would ever know the name of, or understand? Neither he, nor anyone could stop it—no amount of intelligence or love could hold it back."

She also recalls her final few days with the star, a weekend spent together before he took his own life.

"We did all the things we love on Saturday day and into the evening, it was perfect—like one long date. By the end of Sunday, I was feeling that he was getting better.

"When we retired for sleep, in our customary way, my husband said to me, 'Goodnight, my love', and waited for my familiar reply: 'Goodnight, my love'.

"His words still echo through my heart today.  Monday, August 11, Robin was gone."

Schneider Williams hopes that her sharing her tragic experience will help others to understand this hideous illness.

“I have since learned that people with LBD who are highly intelligent may appear to be okay for longer initially, but then, it is as though the dam suddenly breaks and they cannot hold it back anymore," she writes. "In Robin’s case, on top of being a genius, he was a Julliard-trained actor. I will never know the true depth of his suffering, nor just how hard he was fighting. But from where I stood, I saw the bravest man in the world playing the hardest role of his life."

You can read her full essay here.