I tried reading Proust's In Search Of Lost Time some time ago, in which the first 10-20 pages are about a guy lying in his bed at night and observing his own thoughts (roughly). And I quickly realised how I was reading the words and even sentences, but couldn't grasp the meaning of them - I couldn't produce a "mental model" or image of what it was about. It was a very humbling experience.

I used to be an avid reader as a child, even as a teenager. That was a long time ago. I'm looking forward to that time when I will have the mental capacity to read long prose again.