Sinon on peut aussi imaginer un compromis entre les deux : que par exemple le trouble de la personnalité de Saga ait été causé par une malédiction divine ou assimilé sans pour autant être une possession.
The ancient Greeks associated all mental illnesses (depression, schizophrenia, etc.) as an emanation of the will of deities, evil and persecuting, such as Manìa or Lyssa, Dionysus, Hecate, the Furies.
Even in literature, Homer, Sophocles, Euripides describe the insane as possessed by the gods, unbalanced and conditioned in their moods.
And it's for this reason that the madmen in ancient times were not segregated in places, but neither they attempted a therapeutic approach , since it wasn't considered a disease but a punishment received by the gods.
There is a possibility that Kurumada will be informed of these things; after all, another very special clinical case, involving Cain / Abel, was defined as a whim of the gods.