The inability to move your limbs is a frightful experience and amounts to loss of independence of movements. People who have experienced this have their own tales to tell. Some say they recovered almost immediately and continued to function normally soon after. They feel happy and relieved, but the episode forces them to live under constant fear. In technical terms, this is referred to as sleep paralysis.
In the past, sleep paralysis was widely considered to be a work of the incubi [a demon] who was thought to be sitting on the chest of the sleeper or was commonly referred to as a witch riding your back. Recent research has revealed that sleep paralysis usually is a reversible condition but in some instances, it points to a serious sleep disorder.
What is sleep paralysis?
Sleep paralysis basically occurs when the brain awakes from a rapid eye movement [REM] state, but the body paralysis persists. This leaves the person fully conscious, but unable to move from several seconds to several minutes after which the individual may experience panic. Patients find a generalised inability to move their head, body and extremities. In most cases, movement of the eyes and respiratory muscles still occur. Sleep paralysis is most commonly experienced during the onset of sleep [hypnagogic] or immediately after waking up [hypnopompic].
Recurring episodes of sleep paralysis is uncommon in normal individuals. However, up to 40 – 50 per cent of the normal subjects report isolated sleep paralysis at least once in a life time.
Patients experiencing sleep paralysis can see and breathe normally, but are simply unable to move even to a slight extent. They do not realise what is happening to them and hence experience fear and anxiety. It has been reported that these patients even seem to have hallucinations, out-of-body experiences and other such psychiatric manifestations.
What are the causes?
The usual causes are of sleep paralysis are:
- Sleep deprivation
- Sudden environment and/or lifestyle changes
- Narcolepsy [a chronic sleep disorder]
- Unknown ancestral pattern.
Sleep deprivation and stress are common consequences of modern lifestyle. Watching late-night television, coupled with getting up early for work is common in today's life. These practices lead to sleep deprivation. A person who reaches home late from work can also create sleep deprivation in other members of the household [rebound sleep deprivation].
Sleep paralysis is common in narcoleptic subjects and it occurs repeatedly in about 40 per cent of these patients. Narcolepsy is characterised by excessive sleepiness, cataplexy [sudden transient loss or reduction of skeletal muscle tone], sleep paralysis and hypnagogic hallucinations. Evaluation of such patients is necessary and in most cases polysomnography [sleep study] is done for the diagnosis. [See box on polysomnography]
How to manage it?
Sleep paralysis lasts for a few seconds to few minutes and there is spontaneous resolution requiring no further treatment. It has been reported that sleep paralysis occurs in everyone once or twice in a lifetime. But the underlying cause needs to be attended to. Patients who are stressed and sleep deprived need to relax and fulfil their sleep demands. Practising sleep hygiene is of utmost importance in modern day life.
Episodes of sleep paralysis can resolve spontaneously or in response to external stimulation, such as the touch of another person. It is therefore advisable for such patients to sleep with somebody who can help in these situations. Patients of sleep paralysis in whom narcolepsy is suspected need further evaluation.
How is it different from a stroke?
Sleep paralysis needs to be differentiated from paralysis/stroke [for example paralysis of one half of the body or a limb] occurring in sleep or on awakening. Owing to some complex mechanisms the incidence of heart attacks and strokes are maximum during early morning hours. Strokes need careful evaluation and immediate attention. Strokes can also be caused by a sleep disorder called as sleep disordered breathing [SDB], which comprises of snoring, upper airway resistance syndrome and obstructive sleep apnoea [OSA]. SDB is a common disorder and is chiefly manifested by habitual snoring and daytime sleepiness and/or tiredness.
Recent evidence show that treatment of underlying SDB in patients of stroke and heart disease results in better outcomes.
The sleep test
Polysomnography [PSG] is a diagnostic test commonly known as the sleep study. It is a vital test used to rule out sleep paralysis. Various parameters are used in this test, making it more accurate and dependable.
In this test, all the biophysical changes that occur in the patient's body during sleep are recorded. Usually this test is done during the night which is the most natural time when people sleep. However, some laboratories do this test even during the day on people suffering from circadian rhythm sleep disorders.
Other than diagnosing sleep paralysis, PSG is also used to detect many types of sleep disorders like narcolepsy, restless legs syndrome, parasomnia, and sleep apnoea.
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