In this late stage of his illness, he must have been aware that this capacity was deteriorating rapidly, and the panic that caused was worse than any physical pain.

I watched my father go through this (due to Alzheimer’s) before he passed away. He would say “I don’t understand why I just can’t think like I used to”. It was heartbreaking. He was a brilliant mathematician before the disease put him in a mental prison. It was pure torture for him.