Before the eighteenth-century Age of Enlightenment in the west, many individuals and groups were routinely considered to be affected by "demonic possession." This was described as a mental state wherein the individual was not responsible for his actions or words. The victim displayed hysterical symptoms and convulsive writhing that resembled epilepsy, as if a violents struggle were raging within. The face would appear contorted, the body out of control, and there would be an accompanying radical change of vocal timbre: the new and demonic voice was usually deep, gruff, and weird. Often, it spoke languages unknown to it's human host.

The onset of dramatic symptoms was sudden, although there is a suggestion of preexisting states of melancholy in cases of the afflicted. The definite signs were a new shrinking away in horror from religious relics or icons; an ability to speak foreign languages; lewd behavior presumably unknown to the host body; supernatural strength; barking like a dog or fox or bleating like a sheep; and afterward, if the exorcism was successful, no memory whatsoever of the episode by the individual.

To return the possessed to his or her natural state, official rites of demonic exorcism were held by professionals. Since the possession species is worldwide, they continue to be seen frequently in various traditions, and many of the symptoms seem similar throughout the world. The cures or rites are usually in the hands of professionals, but they vary greatly. In India various mantras are uttered and incense is used, in China certain written charms are pasted on the windows and other incantations are burned. Even Josephus, the Jewish historian, in the first century C.E., wrote about a "magic root" that was commonly used among the various practices employed to return the victim to his former self.

In most rites it was of primary importance to "name" the indwelling spirit and then address it directly by name and ask that it leave. In the Catholic Church an official method includes specific wording: "I adjure thee evil spirit in the name of the Lord." This appeal to the specific demonic spirit to leave in the name of Jesus or of various saints was apparently effective. However, when the demon was addressed in this manner its immediate response was spectacular. All hell would break loose. The inhabited person would writhe, vomit, (sometimes spitting out strange objects such as glass, nails, animal hair, insects), and hurl himself/herself around the room, all the while screaming abusively at the exorcist in a gruff, unnatural, hideous voice.

Risks of exorcism were possible contagion-- the "unclean spirit": might move into the body of the priest. Also, the inhabited would sometimes die before the demon was finished struggling. To make matters worse, it seemed that over a few centuries in the West, entire convents or communities were infested. There were epidemics of possession all over Europe. Many of these involved witchcraft and the accusation and torture of so-called witches--all of which are outside the Guide's concern. The Compendium Maleficarum, compiled in 1608 by Brother Maria Guazzo, lists fifty ways in which one can tell if possession is the real thing. Among these notable symptoms are: if the possessed feel as if ants were crawling under their skin; if the body is stirred by palpitations in the afflicted area; if a voice heard inside the head is saying things they don't understand; or if the priest's hand upon their head feels like ice.

Many, but not all, of the indwelling demons who were thought to cause these ravings and crises seem to have disappeared or perhaps shape-shifted and have been identified by other names. In some cases the symptoms are now attributed to various mental illnesses.