Nightmares & Disorders
Sleepwalking and the other things people do while asleep
Parts of the brain wake up and others stay asleep. The result is a person who can walk, cook, drive and hold a conversation while being, in every meaningful sense, unconscious.
Sleepwalking belongs to a family called the non-REM parasomnias, or disorders of arousal, which also includes sleep terrors and confusional arousals. They share a mechanism: an incomplete transition out of slow-wave sleep.
Intracranial recordings in sleepwalking patients have shown this directly. During an episode, motor and cingulate regions show waking-type activity while frontal and parietal association areas remain in slow-wave sleep. The body is up. The parts of the brain responsible for judgement, planning and memory formation are not.
That dissociation explains everything characteristic about the state: the open but glazed eyes, the ability to navigate, the absence of judgement, and the near-total amnesia afterwards.
Who does it
Sleepwalking is common in children — prevalence estimates around 15 to 20 per cent at some point — and usually outgrown by adolescence. Adult prevalence is roughly 2 to 4 per cent.
There is a strong genetic component. Having one sleepwalking parent substantially raises the odds; having two raises them considerably further.
Episodes occur in the first third of the night, when slow-wave sleep predominates, which is one of the most reliable ways to distinguish them from REM-related events.
Anything that either deepens slow-wave sleep or fragments it. Sleep deprivation is the strongest trigger — it increases slow-wave pressure. Also: fever, alcohol, stress, an unfamiliar environment, a full bladder, noise, and sleep apnoea or restless legs, which cause repeated arousals from deep sleep. Some medications, notably z-drugs such as zolpidem, are associated with complex sleep behaviours.
The range of behaviour
Confusional arousals are the mildest — sitting up, looking around, mumbling, appearing bewildered, then lying back down. Common in children.
Sleepwalking proper ranges from wandering the bedroom to leaving the house. People have been found in cars, in gardens, on roads. Injury risk comes from stairs, windows and doors.
Sleep terrors involve a sudden scream, extreme autonomic arousal — racing heart, sweating, dilated pupils — and apparent terror, with the person inconsolable and unrousable. Distressing to observe and unremembered by the sleeper.
Sleep-related eating disorder involves eating during partial arousals, often with unusual food combinations or inedible items, with no memory. It is associated with z-drug use and with restless legs syndrome.
Sexsomnia — sexual behaviour during sleep — is real, documented, and has been raised in criminal proceedings.
The forensic question
Sleepwalking has been accepted as a defence in a small number of serious criminal cases, most famously the 1987 Canadian case of Kenneth Parks, who drove 23 kilometres and killed his mother-in-law, and was acquitted.
Such defences are rare and are assessed against established criteria: a documented history of parasomnia, a plausible trigger such as sleep deprivation, an absence of motive, no attempt to conceal, behaviour of a kind consistent with automatism, and confusion on waking. Sleep laboratory evaluation forms part of the assessment.
These cases are genuinely difficult and are treated with appropriate scepticism by courts. But the underlying phenomenon — complex, apparently purposeful behaviour without consciousness or memory — is not in dispute.
Distinguishing it from REM sleep behaviour disorder
An important distinction, because the implications differ completely.
Non-REM parasomnias occur early in the night, involve open eyes and complex navigation, the person is confused if woken, there is little or no dream recall, they typically begin in childhood, and they are usually benign.
REM sleep behaviour disorder occurs later in the night, involves eyes closed and enacting a specific dream — often fighting or fleeing — the person wakes lucid and can describe the dream in detail, and it typically begins after fifty.
That second one matters a great deal, because it is strongly associated with later development of Parkinson's disease, dementia with Lewy bodies or multiple system atrophy. It requires neurological assessment rather than reassurance.
Management
Safety first. Lock external doors and windows and keep the key elsewhere. Fit stair gates. Move sharp objects and remove trip hazards. Consider a bedroom on the ground floor. A pressure mat or door alarm can alert others.
Remove the triggers. Adequate sleep is the single most effective measure. Regular schedule, moderate alcohol, treat any underlying sleep apnoea or restless legs, empty the bladder before bed.
Scheduled awakening for children with episodes at a predictable time — waking them briefly fifteen to thirty minutes beforehand, for a week or two — has reasonable evidence.
Do not try to wake a sleepwalker. The old warning that it causes harm is a myth; the real problem is that it produces confusion and occasionally an aggressive response. Guide them gently back to bed instead.
Medication — clonazepam or an antidepressant — is reserved for frequent, dangerous episodes, and treating an underlying sleep disorder is usually more effective.
