I’m just reading a thought-provoking book called Hallucinations and Their Impact on Art. Unfortunately, it’s a little dry so isn’t the most gripping of reads but it has this fascinating bit about how hallucinations weren’t considered to be part of madness in the middle ages.
While it is widely accepted in modern times that you can ‘hear voices’ without being mentally ill, the experience of hallucinations is thought to be part and parcel of most forms of madness, whereas this was apparently not the case in medieval times:
What is more curious to the contemporary man is that the medieval description of insanity does not include hallucinations; and the experience of possession (passivity phenomena) is not described as occurring concurrently with or as part of a visionary state.
In Western Europe from AD 500-1500, people who heard voices or saw visions considered themselves, and were considered buy their contemporaries, to have had an actual perceptual experience of either divine or satanic inspiration. They were not considered mad and were not treated as such. Hallucinations (fantasmata) were only considered mad when combined with trickery (prestigiae).
Unfortunately, the book is out of print but it contains many such gems among the rather dull academic prose.