ABC of Sleep Medicine (ABC Series)

Chapter 7

The Parasomnias


·        Parasomnias are unwanted motor or sensory nocturnal phenomena that are usually categorised by the sleep stage (e.g. non-REM or REM) from which they most commonly arise

·        Phenomena such as sudden body jerks at the wake–sleep transition are common as isolated events but can produce more elaborate or complex symptoms that interfere with sleep onset

·        Abnormal partial arousals from the deep stages of non-REM sleep reflect the most common type of parasomnia, affecting up to 20% of children at some point in their development

·        Sleepwalking, night terrors and confusional arousals from sleep probably reflect different manifestations of the same process (i.e. non-REM sleep parasomnia)

·        In adults, non-REM sleep parasomnia activity may lead to antisocial or dangerous nocturnal behaviours that may be ‘goal-directed’ or ‘instinctive’ in the absence of voluntary or conscious control

·        There is very little evidence to guide treatment protocols for troublesome parasomnias

·        Nightmares and occasional episodes of sleep paralysis reflect the commonest forms of parasomnia occurring from REM sleep

·        Prolonged motor activity during REM sleep producing dream enactment is abnormal and may indicate REM sleep behaviour disorder (RBD)

·        RBD is important to recognise as it may reflect the earliest manifestation of neurodegenerative diseases such as Parkinson's disease

·        Several motor phenomena at night disturb the bed partner more than the sleeping subject (e.g. bruxism, nocturnal groaning and fragmentary myoclonus)

Parasomnias are loosely defined as undesirable motor or sensory phenomena arising from sleep itself or the sleep–wake transition. The majority can be explained in terms of an abnormal or inefficient transition from one distinct brain state (i.e. wake, non-REM sleep or REM sleep) to another. Alternatively, elements of one sleep state (e.g. the bizarre or unpleasant visual imagery in REM sleep) can intrude or persist into the wakeful state.

The range of possible experiences and behaviours is enormous, from simple visual images to complex and seemingly purposeful motor activities. Many parasomnias are disturbing both to the subject and bed partner, with fear responses or physical aggression as major components. However, it is not uncommon for subjects to have no subsequent recollection of their nocturnal disturbances, even if complex and prolonged. Some parasomnias are simply ‘annoying’ to the bed partner, with no obvious adverse consequences to the sleeping subjects themselves.

Parasomnias are generally classified according to the state of sleep from which they arise.

Parasomnias at the wake–sleep transition

Hypnic jerks are common slightly unsettling experiences that occur just at the point of sleep onset. Likened to a sudden sensation of falling through space, an abrupt and generalised ‘body twitch’ occurs, occasionally in association with brief a sensory symptom such as a ‘flash’ or ‘explosion’. Although this can cause alarm and produce a degree of sleep onset insomnia, drug treatment is rarely appropriate. Given the possible link to sleep deprivation, advice on sleep hygiene and reassurance are usually sufficient and appropriate.

A rare condition termed propriospinal myoclonus may also cause vigorous jerks whilst lying flat at the point of sleep onset. The movements tend to cause flexion of the trunk and occur on a nightly basis as the subject drifts to sleep. Insomnia may result and be difficult to treat. Occasionally a spinal cord lesion may generate these movements and spinal magnetic resonance imaging is indicated.

Often on a background of head banging or body rocking as young children, some adults may exhibit persistent rhythmical movements as they are dropping off to sleep. This may be viewed as a comforting habit or an aid to sleep onset but, surprisingly, movements also occur during deep sleep and disturb the bed partner. Typical patterns of movement include rolling of the body or slow rhythmical shaking of the head from side to side. Drug treatment is rarely helpful.

Parasomnias from deep non-REM (slow wave) sleep

A spectrum of abnormal behaviours may occur from the deepest stages of non-REM sleep (slow wave sleep) and may affect up to 2% of adult populations. There is usually a history of parasomnia activity in childhood which can range from simple sleep talking or walking to agitated night terrors. A positive family history is also frequently seen.

As with children, this type of parasomnia is thought to reflect partial arousal from the first period of deep non-REM sleep. The subject may appear awake and have open eyes but there is little or no conscious awareness. Recollection of the disturbance the following morning is usually minimal. Behaviours are often benign but can be surprisingly complex and involve navigation through rooms or the use of familiar household objects.

Non-specific fear or agitation is a common association and may cause the subject to shout out or rapidly leave the bed. There is rarely true dream recall although a sense of a ‘presence’ in the room may be reported. Other common themes are visual hallucinations of spiders, for example, or simply a sense of impending doom. In this state, injurious behaviours may result in the rush to leave the room or aggression can be displayed to bed partners, particularly by male subjects.

Compared to children, during non-REM sleep parasomnias adults tend to display more instinctive behaviours that are goal-orientated. Uninvited sexual advances to a bed partner may cause marital disharmony or, at the very least, embarrassment. Similarly, nocturnal eating or cooking with no clear conscious control can be hazardous and also cause excessive weight gain. Some male subjects will regularly urinate in inappropriate places, such as cupboards.

The cause of non-REM sleep parasomnias remains obscure. Although unproven, an abnormality of neurodevelopment or maturation involving the sleep centres in the brainstem appears most plauible. Particularly in adults, factors that deepen sleep (typically sleep deprivation) or inhibit full arousal from sleep (short-acting hypnotic agents) can occasionally trigger parasomnias. Equally, factors that potentially cause partial arousals from deep sleep are often relevant. Examples include an uncomfortable sleeping environment such as a sofa, snoring or extraneous noise, a full bladder, or excessive leg movements. Anecdotally, increased stress or having an ‘overactive mind’ can be a relevant precipitant (Table 7.1).

Table 7.1 Predisposing and precipitating factors in non-REM parasomnias (‘arousal disorders’).


Important factors


Predisposition for non-REM parasomnias (e.g. sleepwalking)

Abnormal maturation of ‘sleep centres’ in brain during early childhood 

The process is presumably under genetic control

Proposed mechanism to explain abnormal partial arousals from deep non-REM sleep 

There is commonly a strong family history of non-REM sleep parasomnias although the nature may vary across generations (e.g. night terrors versus benign sleepwalking);

Relevant genetic linkage studies are awaited

Potential triggers or precipitants

Deeper non-REM sleep than usual

Prior sleep deprivation or previous night shift work are common factors causing deeper non-REM sleep as a ‘rebound’ phenomenon 

Deep non-REM sleep becomes less pronounced by early adulthood potentially explaining why many ‘grow out’ of sleepwalking, for example


Arousals to full wakefulness inhibited

Common examples include CNS depressant drugs such as short-acting hypnotics, alcohol, major tranquilisers or lithium, often in combination


Increased arousals from deep non-REM sleep

Environmental stimuli such as loud noises can be used experimentally to induce sleepwalking in predisposed adults; 

Any cause of ‘secondary insomnia’ can potentially fuel arousals that lead to a parasomnia

Snoring and medical disorders such as oesophageal reflux may predominate in adults

In children, fevers are common triggers


Psychological distress

Increased anxiety levels are often reported as a trigger although systematic evidence is lacking

The role of alcohol as a potential trigger for non-REM parasomnia activity is controversial, particularly if violent or antisocial behaviour has occurred, potentially leading to medico-legal consequences. Significant alcohol intake before bed can certainly influence the nature and quality of any subsequent sleep but no rigorous studies have addressed its specific effects on sleepwalking in those predisposed to the phenomenon. In clinical practice, some subjects report a definite link to excessive alcohol intake whereas others claim it makes them less likely to exhibit disturbances. It seems probable that the secondary effects of excessive alcohol may be particularly important as possible triggers for parasomias. For example, associated sleep deprivation, increased snoring, a full bladder or sleeping in an uncomfortable environment such as the sofa may increase the likelihood of a parasomnia occurring.

It is rare for investigations to help greatly either in the diagnosis or management of non-REM parasomnias unless there is a co-morbid sleep disorder fuelling the situation. It is not uncommon for clinicians to wrongly suspect nocturnal epilepsy as an alternative diagnosis, which may justify overnight polysomnographic recording (Chapter 8 gives more discussion on this differential diagnosis). In a sleep laboratory, it is rare to capture parasomnia events although several sudden arousals from deep non-REM sleep to apparent wakefulness during the night, even in the absence of confusion, may act as a useful marker in those predisposed to the phenomenon (Figure 7.1).

Figure 7.1 The overnight hypnogram of a young adult subject experiencing frequent agitated parasomnias. The arrows at around 2:00 a.m. and 5:00 a.m. indicate two sudden arousals from deep (stage 4) non-REM sleep with brief apparent awakenings and associated confusion. Such arousals are commonly seen in those predisposed to non-REM sleep parasomnias such as sleepwalking.

In this case, there are very frequent periodic leg movements as seen on the PLM trace. These leg movements were important as triggers for the abnormal partial arousals that led to parasomnia activity. Drug treatment of the excessive leg movements resolved the parasomnia.


Although parasomnias are relatively common and potentially dangerous or disturbing, there is very little evidence to guide treatment strategies. Measures such as locking windows or doors may be necessary if events are particularly agitated. Similarly, subjects are encouraged to wear bedclothes to avoid embarrassment in hotels if they are prone to sleepwalking. In general, the avoidance of sleep deprivation and assessment of any underlying sleep disorders causing sleep disruption, such as severe snoring, is advisable. Psychological management of underlying stress may also be appropriate in certain cases.

Given the intermittent nature of parasomnias, it is rare to recommend long-term drug treatment. However, if behaviours are particularly troublesome or frequent, short courses of hypnotic agents such as clonazepam (0.25–1 mg) or melatonin (2–5 mg) before bed may be helpful. Shorter-acting drugs such as zolpidem have been reported to exacerbate the problem and should probably be avoided. Individual case reports suggest that a variety of routine antidepressant agents (e.g. paroxetine) may also reduce non-REM sleep parasomnias although the mechanism remains obscure. If nocturnal sleep eating is the main concern, some authorities recommend the anti-epileptic drug topiramate (25–50 mg nocte). This drug may work by suppressing appetite, thereby reducing the drive to eat during the seemingly automatic state of parasomnia.

Parasomnias from REM sleep


The vast majority of people have experienced occasional nightmares, especially when young. However, episodes frequent enough to cause concern probably affect up to 4% of the adult population. Underlying psychopathology, substance abuse and the use of medications such as beta-blockers may contribute. Post-traumatic stress disorder is strongly linked to recurrent unpleasant dreams related to the original traumatic event.

If necessary, the best management approach is probably psychotherapeutic, using behavioural techniques or even hypnosis. The conscious rehearsal before bed of previous unpleasant dreams engineered to have a ‘happy ending’ is a commonly used technique. However, a course of an agent, typically an antidepressant, to suppress REM sleep may be warranted.

Sleep paralysis

Brief episodes of disturbing paralysis on waking from sleep may be experienced as occasional phenomena in up to 10% of adults. Although very infrequent, the profound loss of voluntary muscle control is so frightening as to be well remembered by most, especially if there are accompanying visual or auditory hallucinatory experiences. The disturbance reflects the persistence of muscle atonia, usually seen in normal REM sleep, into the wakeful state.

In a minority of subjects, the events occur several times a month, often in clusters and occasionally at sleep onset. If necessary, a course of a tricyclic drug such as clomipramine (25 mg nocte) usually helps the situation.

Sleep paralysis in association with severe sleepiness and other REM sleep-related phenomena should raise the possibility of narcolepsy as an underlying diagnosis. This can be particularly disturbing for narcoleptic children and produce a morbid fear of going to sleep (Figure 7.2).

Figure 7.2 A drawing from a six-year-old child with narcolepsy and prominent REM sleep-related nocturnal phenomena, including sleep paralysis.


REM sleep behaviour disorder

Vivid or narrative dreams are most closely associated with the REM sleep stage. In normal REM sleep only the eyes and diaphragm should move. Indeed, descending inhibitory impulses from the brainstem actively inhibit voluntary motor neurons. A subject in REM sleep is completely ‘floppy’ and would be areflexic if examined with a tendon hammer.

In REM sleep behaviour disorder (RBD) this mechanism can fail, causing subjects to literally ‘act out’ their internal dreams (Figure 7.3). This parasomnia affects middle-aged or elderly men in particular and is strongly associated with parkinsonism, even though the more obvious motor features may develop only years later. It is a potential clinical dilemma whether to inform subjects who are diagnosed with RBD in the absence of clinical parkinsonism that they are at greater risk of developing the disease.

Figure 7.3 Two still frames from a video clip showing an elderly gentleman in REM sleep vigorously acting out an aggressive dream.


This finding has led to great interest in RBD as a potential window for looking at early Parkinson's disease and exploring future effective neuroprotective treatments. Recent evidence suggests that the presence of RBD may eventually predict a more complex form of parkinsonism with dementia and psychosis as early features.

The main characteristics of RBD are outlined in Table 7.2. Typical behaviours include lashing out, kicking or punching, often with vocalisation. The subject will generally recall the dream content if awoken during the event. Since REM sleep is usually concentrated towards the end of the night, RBD episodes are often more pronounced at this time.

Table 7.2 Typical clinical features of REM sleep behaviour disorder (RBD).



Elderly males most commonly affected, mean age at presentation is 61

Woman may exhibit a more benign form that presents less often to the clinic

Movements are usually brief and explosive, involving any limb

Injuries to subject or bed partner not rare

Vocalisation is common

Aggressive ‘sleep talking’ may be the first manifestation of RBD

The eyes are usually shut

The subject is simply acting out an internal dream state

Dreams are usually aggressive or ‘sporting’ in nature

The dream aggression usually contrasts with a placid personality during wakefulness

It is rare to leave the bed in RBD

Subjects may well fall out of bed

Any violence is unplanned

Bed partners may be viewed as unfortunate bystanders

If aroused from sleep, subjects usually recall the dream they were having

This contrasts with non-REM parasomnias in which confusion on arousal is the norm

The reasons why RBD affects predominantly males or why the dream behaviours are so aggressive or agitated are unclear. Increasingly, however, more benign behaviours such as laughing or singing are being described. Diagnosis is often very clear from history alone although overnight polysomnography is advocated by many to confirm the presence of abnormal muscle tone during REM sleep periods. The investigation will also help to rule out agitated or confused arousals from severe apnoeas which may mimic RBD in subjects with obstructive sleep-related breathing disorder.

RBD may also be observed in up to 30% of narcoleptic subjects although it is rarely a clinical problem in this group. Occasionally, it can also accompany non-REM parasomnias such as sleepwalking in younger subjects when the term ‘overlap parasomnia’ may be used. Most antidepressant drugs worsen or even induce RBD and should be discontinued if possible.

Given the nature of the problem, long-term treatment is often indicated, if only to prevent injury. There is no controlled data from drug trials but clonazepam (0.25–2 mg) before bed is considered first-line therapy by most authorities. Melatonin (2–10 mg) is increasingly used, especially if clonazepam causes confusion or sedation.

Other parasomnias

A number of parasomnias have been described that have little obvious adverse effect on the sleeping subject but which have the potential to upset the sleep continuity of the bed partner.


Intermittent clenching and grinding of the teeth during sleep may have a prevalence of up to 8% of the adult population. It does not seem to wake or arouse the subject but can lead to abnormal teeth wear and significant facial pain (Figure 7.4). There is also a strong association with migraine and general anxiety.

Figure 7.4 The consequence of excessive teeth grinding in severe nocturnal bruxism.


It can affect any age group and occur from any stage of sleep. Some view it as a non-specific marker of relatively light or poor quality sleep. It is often picked up incidentally as a 1 Hz interference pattern on the EEG trace of an overnight recording.

First-line treatment is usually a dental occlusal appliance rather than drug therapy for which there is no convincing evidence for efficacy.


This is a rare disorder in which subjects emit regular high-pitched monotonous groaning sounds in expiration after prolonged inspiration. It invariably upsets the bed partner and is very difficult to treat. The groans occur in clusters lasting several minutes, often in REM sleep which is otherwise normal.

It can be confused with a form of obstructive sleep apnoea or stridor but, by contrast, has no apparent adverse effects on the subjects themselves.

Fragmentary myoclonus

Some subjects have an increased or excessive tendency for a variety of muscle twitches in the extremities or around the corner of the mouth during light sleep. This subtle phenomenon almost certainly has no major consequence to the sleeping subject and is probably best viewed as a harmless curiosity if picked up from history or investigations.

Further reading

Olson, E.J., Boeve, B.F. and Silber, M.H. (2000) Rapid eye movement behavior disorder: demographic, clinical and laboratory findings in 93 cases. Brain123, 331–339.

Reading, P.J. (2007) Parasomnias: the spectrum of things that go bump in the night. Practical Neurology7, 6–15.

Thorpy, M.J. and Plazzi, G. (2010) The parasomnias and other sleep-related movement disorders. Cambridge University Press.

Wilson, S.J., Nutt, D.J., Alford, C. et al. (2010) British Association for Psychopharmacology consensus statement on evidence-based treatment of insomnia, parasomnias and circadian rhythm disorders. J Psychopharmacol24, 1577–1601.

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