I've zombied myself through a few chapters on countless occasions. Sometimes I get into this mode where I'm just processing information and moving on to the next sentence like it's an entirely new work: process, understand, toss out, go on to next thing.
Sometimes that results in noticing that I don't even remember the last two or three chapters and have to reread.
Sometimes that results in noticing that I don't even remember the last two or three chapters and have to reread.