User blog comment:IamJakuhoRaikoben/Chapter 477: Transport, Review./@comment-7418318-20160314173643/@comment-7418318-20160314174805

Natsu's suffering stemmed from a magic-eating tomour, which Brandish shrinked into practical on-existence. To me that sounds as if all that was necessary for Natsu to recover was resting, while his body stocked up on Ethernano again and also resting to get rid of any lasting after-effects of too low oxygen levels in the blood.

The wounds he got from his fight with Zeref and his underlings didn't seem to be a problem for him at the spring after Happy took him away.