Schneider Williams discussed Williams' unwitting struggle with Lewy body dementia during Tuesday's episode of Today.
Williams died by suicide at age 63 in August 2014. The coroner's report showed Williams had advanced Lewy body dementia, which Williams and Schneider Williams weren't aware of before his death.
"He wasn't in his right mind," Schneider Williams said on Today. "It makes sense why he was experiencing what he was experiencing."
Williams experienced physical and cognitive impairments, anxiety, depression, insomnia and other symptoms before his death. He diagnosed with Parkinson's disease but feared he had dementia or schizophrenia.
Schneider Williams said she felt "relieved" once the coroner's report explained Williams' ailments.
"Robin and I had gone through this experience together, really being chased by an invisible monster. It was like whack-a-mole with the symptoms," she said. "I left there with a name of a disease, the thing Robin and I had been searching for."
Schneider Williams further explores Williams' struggle in the new documentary Robin's Wish, released Tuesday. The film is directed by Tylor Norwood.
On Today, Schneider Williams remembered Williams' humor and care for others.
"This was a man who was incredibly rich and deep and versed in so much about humanity and culture. His humor was like this secret weapon. There were so many times when he would see someone needed a lift and he would just inject a little bit of humor in just the right way to make a difference," she said.
Williams and Schneider Williams married in October 2011. Williams has three children, Zachary, Cody and Zelda Williams, from his previous marriages.