Insomnia had left me with an exceedingly receptive void within my mind. My head seemed made of glass, and the slight cramp in my calves had also a vitreous character.

As soon as I came out of the hotel--Yes, now I think I have found the right words. I hasten to write them down before they fade. When I came out onto the street, I suddenly saw the world as it really is. You see, we find comfort in telling ourselves that the world could not exist without us, that it exists only inasmuch as we ourselves exist, inasmuch as we can represent it to ourselves. Death, infinite space, galaxies, all this is frightening, exactly because it transcends the limits of our perception. Well--on that terrible day when, devastated by a sleepless night, I stepped out into the center of an incidental city, and saw houses, trees, automobiles, people, my mind abruptly refused to accept them as "houses," "trees," and so forth--as something connected with ordinary life.

My line of communication with the world snapped, I was on my own and the world was on its own, and that world was devoid of sense. I saw the actual essence of all things. I looked at houses and they lost their usual meaning--that is, all that we think when looking at a house: a certain architectural style, the sort of rooms inside, ugly house, comfortable house--all this had evaporated, leaving nothing but an absurd shell, the same way an absurd sound is left after one has repeated sufficiently long the commonest word without heeding its meaning: house, howss, whowss. It was the same with the trees, the same with people. I understood the horror of a human face. Anatomy, sexual distinction, the notion of "legs," "arms," "clothes"--all was abolished, and there remained in front of me a mere something--not even a creature, for that is too human a concept, but merely something moving past...

Just as a man who is having a heart attack on a sidewalk does not give a hoot for the passersby, the sun, the beauty of an ancient cathedral, and has only one concern: to breathe, so I too had but one desire: not to go mad. I am convinced that nobody ever saw the world the way I saw it during those moments, in all its nakedness and terrifying absurdity.

Near me a dog was sniffing the snow. I was tortured by my efforts to recognize what "dog" might mean, and because I had been staring at it hard, it crept up to me trustingly, and I felt so nauseated that I got up from the bench and walked away. It was then that my terror reached its highest point. I gave up struggling. I was no longer a man, but a naked eye, an aimless glance moving in an absurd world. The very sight of a human face made me want to scream.

- Vladimir Nabokov, "Terror"

Sounds like a sleep depravation induced form of depersonalization. It's curious how dissociation experiences tend to also involve a deep sense of meaning. It's as if there is a diminished connection to existing pattern memories and the brain is left scrambling to piece together new ones for current stimuli and strongly reinforcing them while at the same time giving negative feedback for the lack of recognition.

The Dissociation wikipedia entry mentions that it can be caused by severe stress. Could it be that the intense negative feedback of high stress (an attempt by the brain to avoid particular behaviors) isn't selective enough in which pattern networks it suppresses resulting in a diminished connections between subsystems?