Robin Williams' widow Susan Schneider Williams has shone a light on her husband's mental and physical struggles during the last year of his life in a powerful personal essay.

Titled "The terrorist inside my husband's brain" and published in the scientific journal Neurology, Schneider details how Williams failed to be diagnosed with the "little-known but deadly" Lewy body disease (LBD) before he died by suicide in 2014. LBD is a form of dementia that most frequently affects the elderly.

"My husband was trapped in the twisted architecture of his neurons and no matter what I did I could not pull him out," she writes.

The couple spent months without a clear diagnosis. Williams was suffering from a variety of seemingly unrelated symptoms in late 2013, including "heartburn, sleeplessness and insomnia." On the set of Night at the Museum 3, he had a panic attack and was finding it increasingly challenging to remember his lines.

"During the filming of the movie, Robin was having trouble remembering even one line for his scenes, while just 3 years prior he had played in a full 5-month season of the Broadway production Bengal Tiger at the Baghdad Zoo, often doing two shows a day with hundreds of lines—and not one mistake. This loss of memory and inability to control his anxiety was devastating to him," Schneider writes.

His journey was long and traumatic, she explains, and it was not until after his death that his LBD diagnosis became clear.

Williams' case was "extreme," Schneider writes: "All 4 of the doctors I met with afterwards and who had reviewed his records indicated his was one of the worst pathologies they had seen.

"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."

After she discovered the culprit, Schneider writes that she was "driven to learn everything I could about this disease." She decided to write the essay to inspire others, and especially doctors, to turn the beloved comedian's experience into something meaningful.

"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," she writes. "Thank you for what you have done, and for what you are about to do."

Williams died in Tiburon, California on Aug. 11, 2014. He left behind three grown children: Zachary Pym, Zelda Rae and Cody Alan.

If you want to talk to someone or are experiencing suicidal thoughts, text the Crisis Text Line at 741-741 or call the National Suicide Prevention Lifeline at 1-800-273-8255. For international resources, this list is a good place to start.