Two years after his death, Schneider Williams penned a heartfelt letter to scientists working to advance research on neurological disorders. In it, she revealed that Williams hid one thing from her during the course of his illness. Read on to learn which heartbreaking symptom Williams endured alone. READ THIS NEXT: Neil Diamond Says Parkinson’s Means He Can Never Do This Again. In the fall of 2013, Williams began experiencing “a firestorm of symptoms,” Schneider Williams recalled. At the time, they seemed unrelated and included “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,” she wrote. Over time, the star also began to experience marked shifts in his mental health, displaying periodic “spikes” in anxiety, delusions, paranoia, insomnia, and fear. In May of that year, he was diagnosed with Parkinson’s disease, though his family would later learn this was a misdiagnosis. “Not until the coroner’s report, three months after his death, would I learn that it was diffuse LBD [Lewy body dementia] that took him,” Schneider Williams explained. “All four of the doctors I met with afterwards and who had reviewed his records indicated his was one of the worst pathologies they had seen.” READ THIS NEXT: This Was the First Sign of Parkinson’s That Michael J. Fox Noticed. Schneider Williams says that at the end of every day, the couple would share their ups and downs. “We would discuss our joys and triumphs, our fears and insecurities, and our concerns,” she explained in her letter. This meant that as time wore on and the actor’s symptoms worsened, they would spend long hours discussing how they affected him. However, Schneider Williams believes there was one thing that her husband held back from her in the months leading up to his suicide: a particular symptom that she believes he couldn’t bring himself to share. “Throughout the course of Robin’s battle, he had experienced nearly all of the 40-plus symptoms of LBD, except for one. He never said he had hallucinations,” she wrote. “A year after he left, in speaking with one of the doctors who reviewed his records, it became evident that most likely he did have hallucinations, but was keeping that to himself.” Only after his death did Schneider Williams realize her husband likely had suffered from hallucinations. In her letter, she shared one heartbreaking memory which suggested that the Julliard-trained actor downplayed his symptoms for his family’s sake. “When we were in the neurologist’s office… Robin had a chance to ask some burning questions. He asked, ‘Do I have Alzheimer’s? Dementia? Am I schizophrenic?’ The answers were the best we could have gotten: No, no, and no. There were no indications of these other diseases,” she recalled. “It is apparent to me now that he was most likely keeping the depth of his symptoms to himself,” Schneider Williams wrote. For more health news sent directly to your inbox, sign up for our daily newsletter. Though she says not having clearer answers was agonizing, Williams’ widow doubts that the actor’s life could have been saved by diagnosis. “Even if we experienced some level of comfort in knowing the name, and fleeting hope from temporary comfort with medications, the terrorist was still going to kill him,” she wrote. “There is no cure and Robin’s steep and rapid decline was assured. It felt like he was drowning in his symptoms, and I was drowning along with him.“ae0fcc31ae342fd3a1346ebb1f342fcb Schneider Williams now serves on the Board of Directors of the American Brain Foundation, and works to raise awareness about the neurological disorder that took her husband’s life. In concluding her letter, she addressed researchers explicitly, imploring them to continue their important work: “This is where you come into the story. Hopefully from this sharing of our experience you will be inspired to turn Robin’s suffering into something meaningful through your work and wisdom,” she wrote. “It is my belief that when healing comes out of Robin’s experience, he will not have battled and died in vain. “I am sure at times the progress has felt painfully slow. Do not give up. Trust that a cascade of cures and discovery is imminent in all areas of brain disease and you will be a part of making that happen,” Schneider Williams wrote. “If only Robin could have met you. He would have loved you.” READ THIS NEXT: The “Crazy” Way Mark Ruffalo Discovered He Had a Brain Tumor.