Sleep paralysis

A paralysed body, a waking mind, and a figure in the room — the same experience reported worldwide, named differently everywhere, and fully explained.

What it is

Waking, or falling asleep, with the body's REM muscle atonia still in force: conscious, aware of the room, and unable to move or speak. Episodes last seconds to a few minutes and end on their own.

The frightening part is what frequently accompanies it:

An intruder — the sense of a malevolent presence in the room, sometimes seen
Incubus — crushing pressure on the chest, difficulty breathing
Vestibular-motor — floating, falling, or leaving the body, which is one of the commonest routes into an out-of-body experience

Around eight per cent of the general population have had at least one episode; rates are higher among students, shift workers, and people with post-traumatic stress or anxiety disorders.

Where it came from

Everywhere, under different names, and the names are the interesting part.

The Old Hag in Newfoundland, studied by David Hufford, who found a detailed and consistent local account of the experience in a community with no medical framework for it
Kanashibari in Japan — "bound in metal"
Ogun oru in Nigeria — nocturnal warfare
Kokma in St Lucia, where the presence is the spirit of a dead infant
Pandafeche in Italy, a cat-like witch
Jinn pressing on the sleeper, across the Arabic-speaking world
The European incubus and mare — the second of which is where the word nightmare comes from, and it is not a horse

Fuseli's The Nightmare (1781), with its squat figure crouched on a sleeping woman's chest, is a straightforward depiction of the incubus form and is probably the most widely reproduced image of a medical condition in Western art.

The medical description is nineteenth century; the physiological account is post-1953, following the discovery of REM sleep.

How it is used

As evidence, in almost every tradition, that something visits people at night. Hufford's argument — in The Terror That Comes in the Night (1982) — is that the traditions were describing a real experience accurately, and that the supernatural interpretation was reasonable given what was known.

What we can and cannot say

We can say the mechanism is understood. During REM sleep the brainstem actively paralyses skeletal muscle so that dreams are not acted out. Sleep paralysis is a dissociation between that system and the systems governing wakefulness: consciousness returns while atonia persists. It sits alongside narcolepsy's other symptoms and can be induced experimentally through sleep disruption.

We can say the intruder experience has a proposed and plausible account. Allan Cheyne's work attributes it to threat-activated vigilance in the amygdala with no external object to attach to: the person cannot move, cannot breathe easily, is aware of the room, and the brain's threat system resolves the mismatch by supplying an agent. The chest pressure is partly the intercostal muscles being paralysed while the diaphragm continues.

We can say the phenomenology is remarkably consistent across cultures while the interpretation is not. The felt experience — paralysis, presence, pressure, terror — is the same in Newfoundland, Nigeria and Japan. What the presence is differs completely. That is the cleanest natural example on this site of a stable experience wearing whatever costume the local culture supplies, and it is worth holding alongside every other claim in this section.

We can say it is harmless in itself and can be genuinely distressing. Episodes are not dangerous. The fear can be extreme, and recurrent sleep paralysis is associated with anxiety and with poorer sleep generally. Regular episodes are worth raising with a doctor — they are a symptom of narcolepsy, and are often improved simply by treating the sleep disruption underneath. This is not medical advice.

And we can say it explains a great deal of other territory. Alien abduction narratives, night visitations by demons, some hauntings, some out-of-body reports and a proportion of "spirit oppression" cases in religious contexts have the same signature: onset at sleep boundaries, paralysis, presence, terror, and a resolution when the person can finally move. Susan Clancy's work on abduction reports found this pattern repeatedly.

We cannot say every such report reduces to this. What we can say is that a specific, common, well-characterised sleep disorder accounts for a category of experience that traditions worldwide have interpreted as visitation — and that the traditions were not making it up.

What it is

Where it came from

How it is used

What we can and cannot say

Further reading