Looking at it from a purely psychological point of view, it makes sense. He meets all of the requirements to have at the very least Undifferentiated Schizophrenia.

Delusions: N is under the belief that it is his sole purpose in life to save all Pokémon from malicious Humans. No matter what he is told, his belief is not swayed. And he is going by any means necessary to try and fulfill this delusion.

Hallucinations: N is experiencing auditory hallucinations, the voices of Pokémon, fueled by his delusion and upbringing.

Possible Ahdeonia: It seems that N derives no pleasure from his everyday activities or things that would normally bring him joy.

Asociality: He is unable to form close, intimate relationships with others, viewing them as numbers in the greater scheme of things.

Avolition: While N has developed a long-term goal, he seems unable to properly plan out and follow through with immediate goals. He shows little interest in forming these goals at all.

N has shown little if any development socially. He is socially awkward and social cues elude him. His intelligence is that of a genius, being able to quickly solve complex mathematical formulas. But his actual mental capacity is that of a child, being naive, innocent, easily excited, and necessitating gentle nudges to move in the right direction, goal-wise.

Genetically predisposed: It is generally accepted that Ghetsis at the very least has delusions of grandeur and is crazier than a barrel full of monkeys.

Not to mention that the stress his childhood caused upon him mentally may have made him more susceptible to the disease and schizophrenic episodes.