For "fell asleep", at least, I think it comes from the word origin. The prefix "a-" in "asleep" comes from an Old English preposition meaning "on," "in," or "into". So "fell asleep" means something like, "fell into a state of sleep". The other two I'm not sure of, but since they are colloquialisms, my guess is that they come from a time when accepted grammar was different or originated from non-standard grammar.

I do not know, but I can say that you are right