Robin Williams' widow on the hidden disease that killed him: "Robin was losing his mind."

Two years on from the death of Robin Williams, the much-loved actor and comedian’s widow, Susan Schneider, has penned a powerful essay about his final months, titled, The Terrorist Inside My Husband’s Brain.

Published in the medical journal Neurology earlier this week, 52-year-old Schneider began, “This is a personal story, sadly tragic and heartbreaking, but by sharing this information with you I know that you can help make a difference in the lives of others.”

Throughout the essay, Schneider focussed on the little-known illness that gripped her husband and ultimately took his life, Lewy Body Disease (LBD).

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Robin Williams in Good Morning Vietnam. Source: Youtube

"When LBD began sending a firestorm of symptoms our way, this foundation of friendship and love was our armor," Schneider said, adding Williams' symptoms began surfacing just ten months before his death.

"He had been struggling with symptoms that seemed unrelated: constipation, urinary difficulty, heartburn, sleeplessness and insomnia, and a poor sense of smell—and lots of stress.

"He also had a slight tremor in his left hand that would come and go. For the time being, that was attributed to a previous shoulder injury... By wintertime, problems with paranoia, delusions and looping, insomnia, memory, and high cortisol levels—just to name a few—were settling in hard," she continued.

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Susan Schneider speaking to Good Morning America following Williams' death. Source: ABC News.

Similar to Alzheimer's, Lewy body disease is a form of dementia that attacks the body's neurons and neurological pathways, affecting cognitive function, alertness, awareness, physical stability and can cause hallucinations.

Sadly it is often misdiagnosed for other illnesses like Parkinson's disease, which is what happened to Williams months before he died.

Since his passing, four separate coroners have all agreed that 62-year-old Williams was one of the worst suffering cases of Lewy body disease they had ever seen.

"Robin was losing his mind and he was aware of it. Can you imagine the pain he felt as he experienced himself disintegrating?" Schneider asked. "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."

"Powerless and frozen, I stood in the darkness of not knowing what was happening to my husband. Was it a single source, a single terrorist, or was this a combo pack of disease raining down on him?"

As the months rolled on, Schneider says, "Robin was growing weary... It felt like he was drowning in his symptoms, and I was drowning along with him. Typically the plethora of LBD symptoms appear and disappear at random times—even throughout the course of a day. I experienced my brilliant husband being lucid with clear reasoning 1 minute and then, 5 minutes later, blank, lost in confusion."

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Robin Williams and Susan Schneider on their wedding day. Source: ABC News.

Having been together for seven years at the time of his death in August 2014, Schneider has tirelessly advocated for greater understanding and the search for a cure of LBD since her husband's' death, which around 1.5 million Americans suffer from.

"Not only did I lose my husband to LBD, I lost my best friend. Robin and I had in each other a safe harbor of unconditional love that we had both always longed for. For 7 years together, we got to tell each other our greatest hopes and fears without any judgment, just safety. As we said often to one another, we were each other's anchor and mojo: that magical elixir of feeling grounded and inspired at the same time by each other's presence," she wrote.

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Robin Williams in Dead Poets Society. Source: Youtube.

"Robin is and will always be a larger-than-life spirit who was inside the body of a normal man with a human brain. He just happened to be that 1 in 6 who is affected by brain disease."

Read the full essay here and learn more about Lewy body disease here