"Social isolation in animals, particularly during critical developmental periods, produces a range of behavioral and neurochemical changes that effectively mimic core symptoms and underlying neural pathologies observed in human schizophrenia patients. This makes social isolation rearing (SIR) a widely used and robust animal model for studying the disorder. "
That's why bears at the zoo pace back and forth endlessly for their entire lives.
Animals can suffer neurosis from mistreatment and other reasons.