It seems to me that the present reference to the Chronica Gallica 452 misrepresents, somewhat, what that document actually says. Let us consider the actual text:
Silvius turbatae admonum mentis post militiae in palatio exactae munera aliqua de religione conscribit.
Silvius, very disturbed in mind following certain munera to the conscript soldiery in the palace, writes upon religion.
The first problem (as it seems to me) is the assumption that this is Polemius, and not some other Silvius. Likely enough, I suppose, given the geography involved, but not certain?
The second problem is that the English "mentally disturbed" suggests insanity to a much greater degree than the Latin turbatae admonum mentis does-- insanity is not excluded, I suppose, but the Latin seems to me, and especially in context, at least potentially to embrace a much wider range of forms of mental distress. Consider that the medieval refrain, Timor mortis conturbat me does not mean (except perhaps very figuratively) that “The fear of death makes me crazy”, but rather that “The fear of death worries /upsets /oppresses me”.
I must at this point admit to some little uncertainty about just exactly what all this Latin means. The cornerstone of my difficulty is that munera (which, it will be noted, I have left untranslated above). I don’t know whether the word here means “duties” assigned to the soldiers, a “gift” or “payment” made to the soldiers, or a “theatrical performance” given for the soldiers. I will also admit to some uncertainty about my "conscript soldiery" for militiae...exactae. Perhaps just "soldiers assigned" in the palace? And I will even admit to a little uncertainty that conscribit de here really means "writes upon".
It seems likely that the entry in the Chronica refers to some story familiar to readers in Southern Gaul around 450, and that its purpose was not to relate that story in any detail, but merely to fix its occurrence in time.
Despite all this, the Chronica entry seems to me far too cool to omit from this article on Polemius. I would, however, propose qualifying the matter by calling the referent "someone named Silvius, quite possibly Polemius", and by saying "very disturbed in mind by certain events" rather than "mentally disturbed".
I hesitate actually to make these changes, but propose them in the hope of prompting action (or clarification) from someone more expert than myself.