Yup. I've fallen asleep reading Braille in bed before. One thing is that the Braille book is on top of the covers, usually on my chest, as I read it with my hands. So I'm not holding the book up so I can see it. When I get tired, my hands move slower, and slower, and slower...and...sleeping. I've woken up in the morning, with the book still open, and on top of me.

Not myself, but a coworker who teaches Braille. He had a student who was learning braille, and regularly came into the classroom early to practice. One time, he comes in, and the student was slouched on the chair, one hand on the Braille and asleep. This was fairly early in the morning.