User blog comment:IamJakuhoRaikoben/Chapter 253: Let's Join Hands, Review./@comment-180.191.109.233-20111002055500/@comment-4078901-20111002055952

Zeref was never in a sleeping state to begin with so he was already awake from the moment he first appeared. Also, I think that Acnologia left since he may have already served his purpose, which is to kill everyone in the island where Zeref summoned him? Although all of this is pure speculation. XD