What is the medical term for the natural paralysis that occurs while a person is in REM sleep? I look it up online, but I only find sleep paralysis which is a misnomer as that actually happens when people are awake in hypnagogic or hypnapompic states. I'm looking for the name of the physiological state of paralysis that happens during actual sleep.
The medical term for the natural paralysis that occurs while a person is in REM sleep – most often cited as 'official' in English – seems to be: REM atonia.
The medical condition associated with hypnagogic sleep paralysis is coded in ICD10 with G47: sleep disorders / G47.4: (according to German Wikipedia) – or G47.8 Other sleep disorders, G83.8 "Other specified paralytic syndromes" (according to English Wikipedia).
Interestingly the German Wikipedia states that Schlafparalyse (=sleep paralysis) is the proper term in German to use with muscle relaxation during real sleep. –– Conscious feelings of paralysis are more often described as "hypgnagoge Schlaflähmung" (= hypnagogic sleep paralyss; but using only true German word components for the compound word)
Im Englischen wird sleep paralysis ausschließlich für die Störung verwendet, während die natürliche Lähmung während des normalen Schlafes REM atonia genannt wird.
(In English sleep paralysis is used exclusively for the disorder, while natural paralysis during normal sleep is called REM atonia.)
REM-atonia in Rapid eye movement sleep:
Organisms in REM sleep suspend central homeostasis, allowing large fluctuations in respiration, thermoregulation, and circulation which do not occur in any other modes of sleeping or waking. The body abruptly loses muscle tone, a state known as REM atonia.
But it doesn't get much better:
MedicineNet –– Medical Definition of Atonia, REM sleep:
Atonia, REM sleep: See: Sleep paralysis
--> Sleep paralysis: Medically, sleep paralysis is sometimes called waking paralysis, predormital (before-sleep) paralysis, postdormital (after-sleep) paralysis, and REM sleep atonia.
In "Unraveling the Mechanisms of REM Sleep Atonia" the phenomenon is called:
We agree with the commentators that determining mechanisms of rapid eye movement (REM) sleep motor atonia is of major scientific importance and clinical relevance. The concept that REM atonia is under the control of one physiological mechanism and one neurotransmitter pathway has seduced many of us.
In summary, it seems that "sleep paralysis" is actually not that far off a choice to use for REM atonia judging by real world word usage. But in any case a further qualification like "during real sleep"?
This excerpt seems to set a very straght record:
Neural mechanisms prevent us from acting out our dreams during REM sleep. This normal “paralysis” during REM known as REM atonia is altered in patients with narcolepsy. Sleep paralysis is the intrusion of the normal atonia of REM sleep into wakefulness. The patient experiences inability to move with preserved aware- ness of surroundings. Sleep paralysis typically occurs during sleep–wake transitions or arousals.
Lourdes M. DelRosso and Romy Hoque: "Central Nervous System Hypersomnias", in Raman K. Malhotra (ed): "Sleepy or Sleepless. Clinical Approach to the Sleep Patient", Springer: Cham, Heidelberg, 2015, p 54.