You're fast asleep

when all of a sudden you're awoken!

And not by your alarm clock.

Your eyes open,

and there's a demon sitting on your chest,

pinning you down.

You try to open your mouth and scream,

but no sound comes out.

You try to get up and run away,

but you realize that you are completely immobilized.

The demon is trying to suffocate you,

but you can't fight back.

You've awoken into your dream,

and it's a nightmare.

It sounds like a Stephen King movie,

but it's actually a medical condition

called sleep paralysis,

and about half of the population

has experienced this strange phenomenon

at least once in their life.

This panic-inducing episode

of coming face-to-face with the creatures

from your nightmares

can last anywhere from seconds to minutes

and may involve visual or auditory hallucinations

of an evil spirit

or an out-of-body feeling like you're floating.

Some have even mistaken sleep paralysis

for an encounter with a ghost

or an alien abduction.

In 1867, Dr. Silas Weir Mitchell

was the first medical professional

to study sleep paralysis.

"The subject awakes to consciousness

of his environment

but is incapable of moving a muscle.

Lying to all appearance, still asleep.

He's really engaged for a struggle for movement,

fraught with acute mental distress.

Could he but manage to stir,

the spell would vanish instantly."

Even though Dr. Mitchell was the first

to observe patients in a state of sleep paralysis,

it's so common that nearly every culture

throughout time has had some kind

of paranormal explanation for it.

In medieval Europe, you might think that an incubus,

a sex-hungry demon in male form,

visited you in the night.

In Scandinavia, the mare,

a damned woman,

is responsible for visiting sleepers

and sitting on their rib cages.

In Turkey, a jinn holds you down

and tries to strangle you.

In Thailand, Phi Am bruises you while you sleep.

In the southern United States,

the hag comes for you.

In Mexico, you could blame

subirse el muerto, the dead person, on you.

In Greece, Mora sits upon your chest

and tries to asphyxiate you.

In Nepal, Khyaak the ghost

resides under the staircase.

It may be easier to blame

sleep paralysis on evil spirits

because what's actually happening in your brain

is much harder to explain.

Modern scientists believe that sleep paralysis

is caused by an abnormal overlap

of the REM, rapid eye movement,

and waking stages of sleep.

During a normal REM cycle,

you're experiencing a number of sensory stimuli

in the form of a dream,

and your brain is unconscious and fully asleep.

During your dream,

special neurotransmitters are released,

which paralyze almost all of your muscles.

That's called REM atonia.

It's what keeps you from running in your bed

when you're being chased in your dreams.

During an episode of sleep paralysis,

you're experiencing normal components of REM.

Your dreaming and your muscles are paralyzed,

only your brain is conscious and wide awake.

This is what causes you to imagine

that you're having an encounter

with a menacing presence.

So this explains the hallucinations,

but what about the feelings of panic,

strangling,

choking,

chest pressure

that so many people describe?

Well during REM,

the function that keeps you

from acting out your dreams,

REM atonia,

also removes voluntary control

of your breathing.

Your breath becomes more shallow

and rapid.

You take in more carbon dioxide

and experience a small blockage of your airway.

During a sleep paralysis episode,

a combination of your body's fear response

to a perceived attack by an evil creature

and your brain being wide awake

while your body is in an REM sleep state

triggers a response for you to take in more oxygen.

That makes you gasp

for air,

but you can't

because REM atonia

has removed control of your breath.

This struggle for air while your body sleeps

creates a perceived sensation

of pressure on the chest

or suffocation.

While a few people experience

sleep paralysis regularly

and it may be linked to sleep disorders

such as narcolepsy,

many who experience an episode of sleep paralysis

do so infrequently,

perhaps only once in a lifetime.

So you can rest easy,

knowing that an evil entity is not trying

to haunt,

possess,

strangle,

or suffocate you.

Save that for the horror films!