Sleep paralysis refers to the phenomenon in which resumption of consciousness occurs while muscle atonia of REM (rapid eye movement) sleep is maintained, leading to intense fear and apprehension in the patient as the patient lies awake without the ability to use any part of their body. It is often accompanied by visual hallucinations of the intruder and incubus variety. Intruder hallucinations involve the perception of a dangerous person or presence in the room. The Incubus phenomenon is characterized by a hallucination with a feeling of pressure on the thorax while carrying out aggressive and/or sexual acts. It tends to be accompanied by anxiety, paralysis, and feelings of suffocation.

The usual phase of the sleep cycle in which it manifests is the REM sleep phase. During Non-REM sleep, there is an increase in parasympathetic tone and a decrease in sympathetic tone, while during phasic REM sleep, there are surges in sympathetic tone. It prevents movement of body parts in response to the dreams and muscles of the body become paralyzed temporarily. If the patient achieves wakefulness in this state, it creates the dissociation between perception and motor control that is characteristic of sleep paralysis.

The prevalence of sleep paralysis in the overall population is estimated to be around 7.6 percent. Males have this condition at a slightly lower frequency than females. Sleep paralysis can begin at any age, but initial symptoms usually show up in childhood, adolescence, or young adulthood. After starting in the teenage years, episodes can occur more frequently in later decades. Prevalence among students and patients of another psychiatric illness is higher. There is also evidence that the prevalence of sleep paralysis is higher in non-White populations.

While there is no established direct causation between a risk factor and sleep paralysis from studies, research has found multiple factors to have some degree of association with this illness. These include anxiety disorders, poor sleep quality, consumption of alcohol, exposure to traumatic events, and a family history of sleep paralysis. A familial association has been established in multiple studies, a fact that hints towards the genetic predisposition of this condition.

The possible explanation for Incubus hallucination during an episode of sleep paralysis is that there is a decrease in respiratory muscle activity during REM sleep; this is due to the inhibition of motor neurons. During REM sleep, respiration becomes irregular, and there is skeletal muscle hypotonia resulting in significant reductions in alveolar ventilation and tidal volume, leading to hypercapnia. In normal subjects, alveolar ventilation during REM sleep can be 40% lower than during wakefulness.

A hypervigilant state is also characteristic of REM sleep, and it appears to originate in the midbrain. This hypervigilance leads to the fear and paranoia that often accompanies these episodes. A possible explanation for REM sleep disorders is flawing in the structures forming the brainstem.

Patients who experience sleep paralysis report that episodes occur before sleeping, upon waking up, and during both times. Most patients also report some stressful events, life and work schedule changes, or an emotional experience preceding the episodes. Physical examination during an episode might reveal all the characteristic features of REM sleep: rapid-eye-movement, muscle atonia, a decrease in respiratory muscle activity, and an increase in the heart rate.

It is important to differentiate sleep paralysis from other similar disorders, including narcolepsy, familial periodic paralysis, conversion disorder, and cataplexy. It also requires differentiation from the symptomatology of PTSD as well as other mental/psychiatric illnesses. This delineation is because these other illnesses are managed by pharmacological and psychological interventions not employed to manage sleep paralysis.

Evaluation

Multiple questionnaires have been developed to aid in the evaluation of sleep paralysis. Some examples include the Sleep Paralysis Experiences and Phenomenology Questionnaire (SP-EPQ), The Unusual Sleep Experiences Questionnaire (USEQ), and multiple questionnaires that assess for the risk factors of sleep paralysis, for example, Beck Depression Inventory, Eysenck Personality Questionnaire, Clinician-Administered PTSD scale, Hamington Anxiety Rating Scale, and Liebowitz Social Anxiety Scale. These questionnaires help determine the triggering factor for these episodes and may aid in the management of this condition.

To date, there is no direct treatment strategy to treat sleep paralysis during an active episode. There have been attempts made to manage the underlying psychological and physical factors that trigger an episode, but currently, there is no treatment available to abort an episode. In one study, Focused-Attention Meditation Combined with Muscle Relaxation (MR Therapy) demonstrated some clinical benefit as a direct treatment for sleep paralysis.

Since a strong correlation exists between sleep paralysis and other sleep problems, improving sleep hygiene is a common focus to help prevent sleep paralysis. Sleep hygiene refers to a person’s daily habits and routines that influence sleep quality. For example:

• Fixed sleep schedule (going to bed and waking up in the morning), including weekends

• The bedroom should have a comfortable mattress and pillow.

• Bedroom with limited intrusion from light or noise

• Keeping a set pre-bed routine, avoid watching TV in the bedroom

• Decrease consumption of caffeine and alcohol, especially in the evening.

• Discontinue use of electronic devices, including cell phones, for at least a half-hour before bed.

Enhancing Healthcare Team Outcomes

Sleep paralysis can be distressing for the patient, as it causes a lot of fear and anxiety, which has shown to worsen the frequency of the episodes, and this loop continues until there is an intervention. Therefore, prompt recognition of the condition and early intervention are vital, and possible psychosocial factors merit attention if present. Sleep paralysis often coexists with other medical conditions, e.g., narcolepsy, idiopathic hypersomnia, obstructive sleep apnea, and insomnia disorder.

Most people have reported managing the episodes by techniques that disrupt the episodes, and few others focus on the prevention of the episodes themselves. Disruption of the episodes seems to mitigate some of the anxiety associated with sleep paralysis episodes; therefore, more and more patients show an inclination towards this mode of management.

Researchers have proposed some treatments for the management of sleep paralysis episodes. Pimavanserin has been a proposed therapeutic intervention in one study as the drug is a selective 5-HT receptor inverse agonist, and thus has the potential to target hallucinations caused by sleep paralysis episodes. Other treatments and management modalities include focussed meditation and muscle relaxation therapies. A combination of the latter two, in theory, has a stronger effect in aborting episodes of sleep paralysis.

No studies have demonstrated any longterm consequences on the health of patients who experience sleep paralysis. While the underlying risk factors may contribute to health-related issues later in life, for example, anxiety poses a risk for hypertension; there is no reported independent association. The episodes of sleep paralysis reportedly come in 'waves,' and the prognosis is good if the triggers are managed effectively in most cases.

Complications

While a benign phenomenon on its own, the heightened fear levels associated with sleep paralysis may lead to anxiety disorders in some patients. It might also cause poor sleep quality, which in turn is a risk factor for sleep paralysis.

Deterrence and Patient Education

Patients require education regarding the benign nature of isolated sleep paralysis. The physician should encourage patients to manage their anxiety through medication and meditation. Another important issue that patients must understand is the hallucinations that accompany these episodes.

These hallucinations often invoke a great sense of apprehension and panic in these patients, and so patients must know their cause, their nature, and their consequences. It is only when patients fully understand the pathophysiology and limited consequences of sleep paralysis will they begin to be less fearful of it, which in turn imparts a positive effect on the prognosis.