The effort of reading comics

I don't think it should come as any surprise that reading a comic takes less of a sort of "work" that is required to read a novel, as evidenced by the fact that I can actually tire myself out with a novel to the point of falling asleep reading it. Just as interesting, though, is the other end -- when I read comics before bed, I find it actively harder to fall asleep, mostly because my brain feels more stimulated or energized. Interestingly, I also tend to fall asleep with a lot of movies nowadays, so maybe comics represent some kind of visual stimulation and textual engagement that provides the most lively experience. I'm basing this conclusion purely on my own reactions -- do other people experience these sorts of media similarly?

I forget where I wanted to take this topic, but it seems to warrant discussion on visual language as opposed to more traditional language. A possible direction is towards some older-school theories about the gaps in literature (not just text/novels) that force the reader to build meaning (I'm thinking Wolfgang Iser over here), and how the (varying) visualness of comics seems to circumvent this requirement.