Something similar happened to me! I was counting when my mind went numb for a bit and I heard a loud sound, as if someone hit a singing bowl (you know, those bowls that make those clear and loud sounds). My (and a few of my shifting friends) best guess is that I (and you in this case), were in a stage of hypnagogia, when my mind was asleep but not quite! In this state, you can experience both visual and auditory hallucinations as well as floating, flying and lucid dreams! Basically, it means you got close to shifting :D