@Tamerlane probably something similar to how patients irl get nutrition and water through IV tubes. They may have similar magic. Also he isn't a human anymore. So maybe it was some sort of hibernation?
Not gonna lie that is one of the most predictable chapters of a Manga that I have ever read. The only thing that surprised me was healing the mom at the end.
@Tamerlane Don't question it, that happens to almost every adventure/fantasy/fighting mc and they're all fine even after sleeping/being unconscious for several weeks without much medical assistance. It's like the karate-hit-behind-the-neck-to-make-them-unconcious thing, it doesn't really make sense but almost every author does that.