Mental illness has always existed, but how it is interpreted and how it presents is socially constructed.

In the modern western world, people with paranoid schizophrenia often interpret their illness in terms of mind control by the CIA, or whatever intelligence agency they happen to be most familiar with. I knew a paranoid schizophrenic in Australia who was convinced that ASIO was trying to poison him with radiation. Microchips and, sometimes, clockwork, are also often part of the delusion.

Those who are very religious interpret their delusions as "demonic possession". In much of Africa, they are interpreted in terms of persecution by witches.

The same mental phenomenon, sleep paralysis, used to be interpreted in terms of "the night hag" while today people are more likely to see "greys" and other alien lifeforms.