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.
当代的科学家认为睡眠瘫痪是由于睡眠的 REM 阶段（快速动眼期）跟清醒阶段的非正常交错而引起的。
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!