I once watched all the endless eight episodes of Melancholy of Harhuhi Suzumiya in one sitting.

For those that don't know these episodes deal with the characters being stuck in a timeloop thats resets their memories. Eventually the sense of de ja vu lets them know about the timeloop and grows more intense with each reset. There are slight differences in each of the 8 episodes except for the first and last.

The sense of de ja vu that I felt matched that if the characters, and a sense of wrongness when a character said a line slightly differently or a different character said that same line is hard to describe.

I doubt I'll do it again but it was pretty intense for what it was.