This is more common than you might think. There is a whole online community of people who have persecutory delusions called Gang Stalking. There was a podcast of a woman who's whole childhood she grew up constantly randomly moving and cutting contact with family because her mom's boyfriend suffered from this mental illness, and convinced the mother she too was being followed.

It's like the primate part of the brain that says "there's a predator in those bushes" is always stuck in the ON position.