[Recapping the bottle, Nagisa transfers it to his pocket for now. He'll go put it back in the box later. First, he needs to make sure Jataro is okay.]

I guess it could be your brain changing. It seems as though there are a fair number f psychological changes to accompany the physical ones. Perhaps headaches are a common side effect of such changes. Though... [He raises his hands and shakes his head.] I doubt you need to worry about your brain rotting out. I've yet to see or hear of an undead monster that was truly mindless like a stereotypical zombie.

[He frowns, lifting a hand back to his lips, not to feel it for lipstick this time but in contemplation.]

Where exactly does it hurt? What part of your head, I mean.