Paul Broks at Literary Review:
Madness is deep-rooted in the human imagination. The mad are unreachable, unfathomable, alarmingly other. They unsettle us. Yet we also romanticise madness. Great poetry and art spring from transcendent states at the edge of sanity, don’t they? And falling in love is a kind of madness, a stumbling into a dream world of irrationality and delusion. The lunatic, the lover and the poet are of imagination all compact. One line of thought is that madness is the price Homo sapiens has paid for the jewel of human consciousness. Perhaps it is.
There have always been alienated individuals marked out as ‘mad’ by the rest of society on account of their bizarre beliefs and eccentric behaviour, but it was not until the late 19th century that Emil Kraepelin established a formal taxonomy of signs and symptoms.
more here.