[The "but" is real...]

Try out a purification method, probably. After all, if you start showing physical symptoms, a protective charm isn't going to do much.

[Casually discussing the possibility of impending possession, as one does.]

Those don't require any blood or even any writing at all, at least! Just salt. ...Well, it should be a little more than just salt in an ideal situation, but I doubt I'll find what I need here.