Thing is that you cannot "sleep something". The only transitive sense (i.e. when the verb has a direct object) is when you "sleep with someone" (i.e. have sexual relations with that someone). You cannot, however, "sleep a book" - which is what is being formulated in >>44.

I suppose one could go to sleep with a book, so to speak, when one reads it before going to sleep and then falling asleep while reading it. That's still not expressed in >>44 either, though.

Maybe what was meant to be said was: "It's difficult to go to sleep when reading that book", meaning that going to sleep is a difficult task when you are busy reading the book.