Dr Buzzi is a practicing neurologist with a special interest in sleep disorders,including sleep paralysis, with a private practice in Ravenna, Italy. He has co-authored numerous publications in the fields of sleep apnea and restless legs syndrome.
Occasionally, during sleep, I start to wake up . . . or try to force myself to wake up. During these episodes, I can hear what is going on around me, but I’m unable to move or open my eyes. I’m not completely awake, but I’m not really asleep either. It’s an extremely frightening and stressful incident when it occurs. I’m wondering if this is normal—not being able to move is almost painful, as I can feel my muscles fighting to move and they can’t.
Clinical presentation and physiopathology
Sleep paralysis (SP) is quite easy to recognize once there is some familiarity with the disorder. Clinically, it is characterized by a transient inability to move or speak at sleep onset or upon awakening. The episodes last seconds to several minutes, and termination is spontaneous or induced by external stimulation (eg, if the subject is touched by another person). The patient may be unable to open their eyes and have a feeling of suffocation, although ocular and respiratory movements are usually intact. SP is commonly associated with intense fear and anxiety, which may be enhanced by the concomitant occurrence of multisensorial hallucinations. These hallucinations typically include an intruder (eg, a threatening presence; see Figure 1, Case Example 1) and an incubus (eg, a malevolent agent exerting pressure by sitting on the chest).
During SP, the patients are awake or half-awake, with varying degrees of awareness; they usually engage in a mentl struggle to move or to cry out, yet they appear to be sleeping. They may experience a false awakening phenomenon (seeFigure 1, Case Example 2).
SP may occur in an isolated form (ie, isolated sleep paralysis or ISP) or in the context of narcolepsy. Recurrent isolated sleep paralysis (RISP) is the recurrent form of ISP; it is listed by the International Classification of Sleep Disorders (ICSD) as a REM sleep-related parasomnia.
Sleep paralysis and associated hallucinations occur when REM sleep elements (such as muscular atonia and dream imagery) intrude into waking, with an overlap between the two states. SP can be facilitated by sleep schedule alteration, mental or physical fatigue, stress, shift work, jet lag, alcohol, sleep disrupting medication. These factors cause sleep disruption with frequent awakenings, facilitating REM-wake overlap, and/or REM sleep deprivation with subsequent REM rebound with enhanced dreams at sleep onset. SP is also more likely to occur when the subject sleeps in a supine position.
SP and associated hallucinations have been interpreted in a variety of cultural contexts, with supernatural explanations ranging from malevolent spirits to alien encounters. As such, some patients may be reluctant to report these events.
Recent areas of interest
Recent research has focused on epidemiology, risk factors and neurocognitive aspects of this condition; the latter will not be considered in this brief overview (for more information, please see this report).
A systematic review1 of SP prevalence found that 7.6% of the general population experienced at least one episode of sleep paralysis, with higher prevalence rates in students (28.3%) and in psychiatric patients (31.9%). In particular, 34.6 % of the patients with panic disorder reported lifetime sleep paralysis. The authors speculated that irregular sleep patterns, which is a risk factor for SP, are often associated with students and psychiatric patients and thus may be related to the higher prevalence rates in these populations. It should be noted that this study was unable to ascertain rates of recurrent SP or isolated SP (ie, SP not related with narcolepsy or other disorders).
1. Sharpless BA and Barber JP. Lifetime prevalence rates of sleep paralysis: a systematic review. Sleep Med Rev. 2011;15: 311-315.
2. Denis D, French CC, Rowe R et al. A twin and molecular genetics study of sleep paralysis and associated factors. J Sleep Res. 2015;24: 438-446.
3. Denis D, French CC, Gregory AM. A systematic review of variables associated with sleep paralysis. Sleep Med Rev. 2018;141-157.
4. Sharpless BA, Doghramji K. Sleep paralysis: Historical, Psychological and Medical Perspectives. New York: Oxford University Press; 2015.