Robin Williams’ widow has shared private info about the actor’s last months, describing how a rare brain condition stripped him of his sanity in devastating detail.

Williams’ third wife, Schneider, writes about her late husband’s fight with Lewy body dementia, which was misdiagnosed as Parkinson’s disease two months before his death and led to his suicide in August 2014.

Susan wrote about the events leading up to her husband’s death in an essay titled “The Terrorist Inside My Husband’s Brain” for the medical journal Neurology. She wrote: “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.”

“It felt like he was drowning in his symptoms, and I was drowning along with him,” she says.

Schneider Williams goes into great detail on the effects of the sickness on him, including sleeplessness, tremors, anxiety, stomach issues, substantial memory loss, and paranoia.

She writes, “Robin was growing weary. The parkinsonian mask was ever present and his voice was weakened. His left hand tremor was continuous now and he had a slow, shuffling gait. He hated that he could not find the words he wanted in conversations. He would thrash at night and still had terrible insomnia. At times, he would find himself stuck in a frozen stance, unable to move, and frustrated when he came out of it. He was beginning to have trouble with visual and spatial abilities in the way of judging distance and depth. His loss of basic reasoning just added to his growing confusion.”

Schneider says, “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”.

“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?”

Schneider’s symptoms were so bad that he wished to “reboot” his brain, according to Schneider.

“He kept saying ‘I just want to reboot my brain.'” Susan added.

Williams was ultimately diagnosed with Parkison’s disease, but this did not provide answers to many of the unanswered concerns that had been circling his mind.

“Everything came back negative, except for high cortisol levels. We wanted to be happy about all the negative test results, but Robin and I both had a deep sense that something was terribly wrong.

During the production of “Night at the Museum 3,” Schneider recalls having difficulty “remembering just one line.”

“In early May, the movie wrapped and he came home from Vancouver — like a 747 airplane coming in with no landing gear,” writes Schneider. “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. 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.”

While Williams never told his wife that he was having hallucinations, which are a common sign of LBD, a doctor told Schnieder after he died that he was likely to have had hallucinations but decided to keep silent about them.

Williams hanged himself at their Tiburon, Calif., home on Aug. 11, 2014, after three years of marriage. He died of asphyxiation and Lewy body dementia, which is caused by protein deposits in the brain, according to the postmortem results.