This is the first, and probably most relevant, post in the Things that Go Bump section for a reason. Nightmares, or more generally, Spiritual Parasites, are the most common form of hostile spirit, and most people have had numerous brushes with them without knowing it.

When a person’s body dies, the ghost left behind is held together by a kind of “life energy” that was produced constantly by human beings. Think of it as a kind of fuel, like a car with gas. A ghost can do all kinds of things, alter its form, move around, and just continue to exist, but it all consumes this energy. Most commonly, a spirit will see no further reason to stick around in the world, and it will stand around doing nothing until it runs dry and fades away. There are other ghosts, I would estimate around 5%, that seek out ways to gain more energy. Most common out of all of those are spiritual parasites.

A living human being is a rich source of life energy, because it is continually replenished by the living body and the experiences and emotions of the living person’s “soul”. Parasitic ghosts are ghosts that, in life, experienced or created one kind of emotion or feeling so much or so exclusively, that they can actually tap into and consume that kind of energy in death, enough to “fuel” themselves indefinitely. For example, a ghost who, in life, was a rich wall street trader and who was obsessed with greed and the gaining of money and power might be able to feed off the greed of others.

The most common of these emotional parasites are Nightmares, spirits who feed off of fear. For some reason, fear seems to be a rich source of energy for these ghosts, allowing them to take hold of a living host for a shorter period of time and then leave to find another. Most other types of parasites try to “hang on” to a single host as long as possible, until dislodged by accident or purposefully by the host.

An interesting note about parasites and other “purposeful” ghosts is that they do not retain the physical structure they had in life. A normal, inactive spirit will look very much the same as it did in life, while an active spirit will morph its form to serve its new purpose. Parasitic ghosts seem to change in two patterns, with every one unique somehow. Either they will remain human-sized and upright, and develop long, tentacular hands and fingers that the spirit will wrap around its host, or it will become much smaller, crouching on all fours and latching onto the body of the host. This really has no practical application, I just think it’s kind of interesting.

For information on how to diagnose a spiritual parasite, defend oneself against them, or forcibly remove one when it has latched on, see the section titled “AAAAAAAAAAH! How can I defend myself?”