User blog comment:Miskos3/Fairy Tail 512: Sting, the White Shadow Dragon, Review/@comment-130.105.140.154-20161130081519/@comment-7418318-20161201083919

Yes we don't know how much time passed between Natsu's demonification/ressurection and him being handed over to Igneel, but we do know that this phase can't have lasted long.

We see how Natsu looked right after his revival, we know how he looked when he met Igneel and we know that he ages at a normal Human pace. Combine those three and we can posulate that the period of uncertainty can't have been long.

Not to mention that Natsu isn't exactly the brightest, so unless he has a split personality with the Demon side not just being different in behaviour but also in intelligence, I can't imagine Natsu inventing a new magical concept like a Curse.