It may feel unsettling that our body goes into a state of paralysis during sleep, but this is a normal and protective part of the sleep cycle. The phenomenon, known as sleep paralysis, occurs when a person becomes conscious but is unable to move. While varying in intensity, the experience is generally uncomfortable and rarely desired.
The exact mechanism behind sleep paralysis remains a subject of ongoing research. Most experts link it to the rapid eye movement (REM) stage of sleep, the period when vivid dreams occur. During REM, the brain induces muscle atonia— a temporary paralysis of the skeletal muscles— to prevent us from physically acting out our dreams. This protective measure also inhibits many reflexes that rely on voluntary muscle control.
One reflex notably affected is sneezing, an evolutionary response designed to expel foreign particles from the nasal passages. While awake or in lighter sleep stages, the body can detect irritants, trigger the trigeminal nerve, and coordinate the diaphragm, chest, and vocal cords to force air out. However, in REM sleep, the same neural pathways that prevent dream enactment also suppress the sneeze reflex, rendering sneezing impossible during this phase.
REM sleep is not the deepest sleep stage, yet it is a profound one. During this period, the central nervous system is surprisingly active, yet the skeletal motor system is put into a state of muscle atonia. The precise biochemical pathways that establish this paralysis have been studied extensively.
A landmark 2012 study published in the Journal of Neuroscience investigated REM atonia in rats and identified two key neurotransmitter systems that collaborate to induce muscle paralysis: gamma‑aminobutyric acid (GABA) and glycine. These chemicals inhibit the brain cells responsible for initiating muscle activity, effectively silencing the motor output during REM sleep.
As research continues, scientists are uncovering more about the intricate balance between REM sleep’s protective paralysis and the maintenance of basic bodily functions. During REM, individuals are not only prevented from moving but also from coughing, feeling hunger, hiccupping, or sneezing.
While the suppression of sneezing during REM may seem counterintuitive—especially when considering the body’s need to clear nasal passages—this effect is temporary and confined to the REM stage. In lighter stages of sleep, the nasal mucosa can still sense irritants, momentarily awakening the individual to trigger a sneeze. The complete paralysis of the sneeze reflex during REM is a direct consequence of the same neural mechanisms that prevent dream enactment.
Understanding the science behind REM paralysis not only demystifies the occasional discomfort of sleep paralysis but also highlights the intricate safeguards our nervous system employs to protect us during sleep.
