Starting from episode 1 i was wondering about this question, but i couldn't find an answer until the latest episode (i might've overlooked sth., though).

Does the human body of Momonga transformed itself into his character in the game?(consequently his soul should be in this character)

Or is it sth. similar to SAO where his original body is still in the "human-world", but his soul in the "game-world"?

Or could it be that Momonga is with his soul and human-body in his own world and sits in front of his computer playing this realistic game?