I start salivating a lot when I read

Kind of a weird question but have no explanation for this strange phenomenon. I've been reading a lot of science fiction/fantasy books for several months now, and for the past week, as soon as I start reading, my mouth waters a lot, as if I'm about to vomit. I can read for hours, and nothing helps, it just keeps happening.
I've tried eating and/or drinking before reading, and reading in different positions, but it doesn't change anything. It's not particularly serious, but it's annoying.
I should mention that I'm not under any particular stress or in any physical condition that could cause this. Whether I'm on the subway, on my deck chair, or in bed, it's exactly the same every time.

And it only happens when I'm reading. In no other aspect of my life have I experienced anything similar.

Has anyone else experienced this?