About mental diseases and kamma
I knew someone who was diagnosed as psychotic for most of her adult life. Psychiatric medicines were semi-effective in her case (so the psychiatrist called her "one of the lucky ones"), so apparently the symptoms were brain-related -- even if etiology is too complicated i.e. physical and environmental.

A couple of comments based on that...

It took years before finding how to get medical treatment, because she was never "an imminent danger to self or others" which is the usual legal requirement for imposing medical treatment. I interpret that as evidence that her intentions toward others were invariably or mostly kindly, even when her thinking was very confused (disordered in form and content). To the extent that "kamma is intention", I think that counts for a lot.

She expected to be reborn; but she didn't say where nor for how long.


MN 57 says something about being reborn as an animal -- given her great sympathy for ("mind of goodwill towards") animals, perhaps that (rebirth in the animal realm) is a possibility.
Conversely her "sins", such as those ever were, were all too human -- perhaps that means a human rebirth.
Perhaps she visited other realms (brahma- and otherwise) "in this life", experienced "paranormal entities" -- to that extent perhaps she developed some equanimity about future experiences.