I initially thought this was just a function of reading the same thing multiple times, but I’ve since had it happen many times when reading something completely new. Somehow my mind wanders and when I tune back in, not only am I reading clearly, I’m still doing the voicing for different characters. It’s so weird.

I haven't had it happen while reading aloud (since I almost never read aloud), but I've definitely had it happen while reading something new that I hated. I'd end up having to read the same page (or more!) three or four times because I kept zoning out.