W.Y. Evans-Wentz - The Fairy-Faith in Celtic Countries - The Sun and the Moon and being 'moon-struck'
Type of spiritual experience
This observation is fascinating as it incorporates the symbolism of the Sun and Moon, but provides an explanation for illnesses like schizophrenia.
It may not be the 'right' explanation, but it does provide a better explanation than many of the medical ones, which appear to revolve around the idea that it is a product of the person's imagination.
This is saying that it is a product of 'angry souls' [angry for whatever reason] seeking a body.
A description of the experience
The Fairy-Faith in Celtic Countries, by W.Y. Evans-Wentz, 
The Rev. T. M. Morgan, Vicar of Newchurch parish, near Carmarthen, …contributes additional material about the Doctrine of Reincarnation in South Wales:--
'My father said there used to be expressed in Cardiganshire [a belief in reincarnation]. This was in accord with Druidism, namely, that all human beings formerly existed on the Moon, the world of middle Light, and the Queen of heaven; that those who there lived a righteous life were thence born on the Sun, and thence onward to the highest heaven; and that those whose moon life had been unrighteous were born on this Earth. Through right-living on Earth souls are able to return to the Moon, and then evolve to the Sun and highest heaven [Stars – Milky Way]. ….
The Goddess of Heaven or Mother of all human beings was known as Brenhines-y-nef. I am unable to tell if she is the Moon itself or lived in the Moon. On the other hand, the Sun was considered the Father of all human beings.
According to the old belief, every new Moon brings the souls who were unfit to be born on the Sun, to deposit them here on our Earth.
Sometimes there are more souls seeking embodiment on earth than there are infant bodies to contain them. Hence souls fight among themselves to occupy a body. Occasionally one soul tries to drive out from a body the soul already in possession of it, in order to possess it for itself. …..
Whenever such a condition showed itself, the person exhibiting it was called a Lloerig or "one who is moon-torn"--Lloer meaning moon, and rhigo to notch or tear; and in the English word lunatic, meaning "moon-struck", we have a similar idea.'