I agree that fever and lack of sleep can produce hallucinations, but I'm not convinced that they are non-localized effects in the brain, nor that psychedelic chemicals are non-localized in the brain.
How do you think the temperature increase from Fever could be localized? It's just a temperature increase and you can induce the same effects by preventing the body from cooling down effectively.
I meant the effects of fever, so that perhaps different parts of the brain was affected differently by the temperature increase. I really have no idea, but I was saying that it is not an obvious fact either way.