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Hypnagogic (Predormital): This happens while you are falling asleep. As your body relaxes, your mind remains conscious, noticing that your voluntary muscles are already shutting down.
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Hypnopompic (Postdormital): This occurs upon waking up. During the Rapid Eye Movement (REM) phase of sleep, your brain actively dreams while keeping your muscles immobilized. If you wake up before the REM cycle finishes, your mind regains awareness before your body regains mobility.
The Biological Mechanism: Why the Body Shuts Down
To understand why this immobility occurs, it helps to take a closer look at the architecture of human rest cycles. The body alternates between Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM) states.
The Role of REM Atonia
During REM sleep, your brain is highly active, processing vivid dreams. To prevent you from physically acting out these dreams—which could lead to accidental injury—your brain signals your motor neurons to relax completely. This state of temporary paralysis is called REM atonia.
During a typical night, two specific neurotransmitters are released to maintain this state:
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GABA (Gamma-Aminobutyric Acid)
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Understanding Sleep Paralysis: The Science Behind Nocturnal Immobility
