Science Behind Sleep Paralysis: Why Can’t We Move Our Limbs In Sleep?

Imagine waking up in the middle of the night, startled by a terrible nightmare that you had. You try to reach out for the bottle of water next to your bed, but you realize that you are unable to move a single muscle in your body, let alone reach out for that precious bottle. You cry out for help, but your voice fails you.

In the moments that follow, you sense the presence of a sinister spirit inside your room. It can be anywhere – the foot of the bed, by your bedside, or even sitting on top of your thumping chest. You try to fight off the paralysis with every fiber of your being and ounce of concentration, but your efforts are vain. You try to go back to sleep, but the electric hum doesn’t let you. You are unable to breathe. In fact, you feel like you’re about to have a heart attack.


This is one version of what it feels like to experience a sleep paralysis episode. Pretty scary, right?

What exactly happens to our system when such episodes occur?

To explain this strange phenomenon, we need to have a basic understanding of something called REM sleep. REM sleep, or Rapid Eye Movement sleep, is a phase that occurs during sleep that is characterized by random movement of the eyes, no control over voluntary muscle movement, and the susceptibility to dream vividly.


the sleep cycle(

During sleep, our bodies go through five 90-minute cycles of alternating REM (Rapid Eye Movement) and NREM (Non-Rapid Eye Movement) sleep. During the NREM sleep, our body relaxes, strengthens the immune system and regenerates tissues.

Sleep paralysis demon

Hallucinations during sleep paralysis

Here comes the interesting part: Sleep paralysis occurs when a person wakes up before the REM stage has been completed, leaving them in a paralyzed state, but enabling them to be aware of their surroundings.

Furthermore, since REM sleep is associated with our dreams, the paralysis keeps people awake, even as impossible dream episodes continues playing inside their heads. Hence, the person experiences auditory and sensory hallucinations.

The Culprits Behind this Phenomenon

Two chemicals of the brain, namely glycine and GABA, help the muscles stay paralyzed during REM sleep. These two chemicals send signals between brain cells, which switches off the neurons that allow the muscles to be active.


Functioning of GABA.

Sensing an intruder may be caused by the combination of lower sensory detection thresholds and high activity in the amygdala (the emotional center of the brain).

Breathing difficulty during a sleep paralysis episode is due to paralysis of the muscles in the upper airways, which causes those feelings of choking and suffocation.

Hallucinations, both sensory and auditory, are very common when sleep paralysis occurs. A waking nightmare sounds pretty awful… I certainly wouldn’t want to experience this, or else I’d end up being an insomniac!


  1. Sleep Paralysis – Wikipedia
  2. Live Science
  3. Scientific American
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About the Author:

Ishan is a Mechanical Engineer from Mumbai University, India and is obsessed with science, food and all things football. He is a self proclaimed cyclist, runner and a professional procrastinator.

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