Dreams, nightmares and things that happen in the night

The things that happen during sleep divide neatly by which part of the night and which stage they arise from, which is more informative than it sounds.

The two families

Non-REM parasomnias arise from deep slow-wave sleep, which is concentrated in the first third of the night.

They include sleepwalking, confusional arousals, night terrors and sleep-related eating.

The characteristic features: the person is not fully conscious, is difficult to rouse, and typically has no memory of it afterwards.

REM parasomnias arise from the dreaming stage, concentrated in the second half of the night.

They include nightmares, sleep paralysis and REM sleep behaviour disorder.

Here the person generally can be woken and generally does remember.

Sleepwalking and night terrors

Common in children and largely outgrown, with a genetic component that runs in families.

Night terrors involve sudden apparent panic — screaming, sweating, wide eyes — with no recall afterwards, which is far more distressing for the observer than for the child.

The advice is not to wake them, since that produces confusion and agitation, but to keep them safe and let it pass.

Triggers in adults and children include sleep deprivation, fever, alcohol, some medications, stress and anything fragmenting sleep, including sleep apnoea and restless legs.

Which means the effective response is usually to address the trigger and to make the environment safe: locking external doors, securing windows, removing obstacles and stairs where possible.

Persistent or dangerous episodes in adults warrant assessment, since new-onset sleepwalking in adulthood is less common and more likely to have an identifiable cause.

Nightmares

Distinguished from night terrors by the recall and the timing.

Occasional nightmares are universal.

Frequent nightmares causing distress or affecting sleep constitute nightmare disorder, and are strongly associated with post-traumatic stress disorder, where they are a core symptom.

Contributors include certain medications, alcohol and its withdrawal, and REM rebound after any REM suppression.

The treatment with the best evidence is imagery rehearsal therapy: rewriting the nightmare's narrative while awake and rehearsing the new version repeatedly, which has good trial support including in trauma populations.

Certain medications are used where nightmares are trauma-related, with evidence that has been debated.

Sleep paralysis

Frightening, harmless, and much more common than people assume.

During REM sleep the body is paralysed to prevent acting out dreams.

Sleep paralysis occurs when consciousness returns before that paralysis lifts, leaving the person awake and unable to move, frequently with a sensation of pressure on the chest and, in a substantial proportion of episodes, hallucinations of a presence in the room.

These hallucinations are the likely origin of a great deal of folklore across cultures, which is worth knowing during an episode.

It is associated with sleep deprivation, irregular schedules, sleeping on the back and stress, and it lasts seconds to a couple of minutes.

Frequent episodes with excessive daytime sleepiness should prompt assessment for narcolepsy.

REM sleep behaviour disorder

The one that matters most and is least known.

Here the paralysis of REM sleep fails, and the person physically enacts their dreams — punching, kicking, shouting, leaping from bed — frequently injuring themselves or a partner.

It occurs mainly in older adults and more often in men.

The important point: longitudinal studies have found that a high proportion of people with this disorder go on to develop a neurodegenerative condition such as Parkinson's disease or dementia with Lewy bodies, sometimes years or decades later.

It is therefore a recognised early marker rather than an isolated sleep problem, and it warrants specialist assessment rather than reassurance.

Management includes making the sleeping environment safe and specific medications.

Other night-time events

Hypnic jerks — the sudden whole-body twitch as you fall asleep — are universal and benign.

Exploding head syndrome, an alarming name for a harmless sensation of a loud noise as you fall asleep or wake.

Sleep talking, common and meaningless.

Teeth grinding, which damages teeth and warrants a dental guard, and which is associated with stress and with sleep apnoea.

And nocturnal leg cramps, distinct from restless legs, which are common and generally benign.

When to seek help

Injury to yourself or a bed partner.

Behaviour that puts anyone at risk, including leaving the house.

New-onset parasomnia in an adult.

Dream enactment, specifically, given what it may indicate.

Frequent nightmares causing distress, particularly after trauma.

And any of these accompanied by loud snoring or daytime sleepiness, since treating an underlying sleep apnoea frequently resolves the parasomnia entirely.

General information only, not medical advice. Consult a qualified clinician about dream enactment, injury during sleep or new parasomnias in adulthood.