Hypnagogic hallucinations

What are hypnagogic hallucinations?

Hypnagogic or hypnopompic hallucinations are visual, tactile, auditory, or other sensory events, usually brief but occasionally prolonged, that occur at the transition from wakefulness to sleep (hypnagogic) or from sleep to wakefulness (hypnopompic).¹

The phenomenon is thought to have been first described by the Dutch physician Isbrand Van Diemerbroeck in 1664.²

Previously, visual hallucinations were thought to be the most common, but recent studies suggest that kinaesthetic hallucinations, such as the feeling of a presence in the room and the feeling of falling, are as common as visual hallucinations, and both are more common than auditory hallucinations. ¹

Their cause is unknown. Neurobiological factors associated with REM sleep have been postulated but there is little evidence. ³

• Hypnagogic hallucinations are common in the general population.⁴ Up to 77% of people report at least one hypnagogic hallucination. ¹

• A UK study showed that 37% of the sample reported experiencing hypnagogic hallucinations, and 12.5% reported hypnopompic hallucinations.⁵ Both types of hallucinations were significantly more common among subjects with symptoms of insomnia, excessive daytime sleepiness or mental disorders.

• A more recent study from Norway reported hypnagogic hallucinations in 9% of the general population. ⁴

• The same study showed that, of the hallucinations reported, 6.8% of people had hallucinations in the auditory domain, whereas 12.3% reported multimodal hallucinations, and 32.2% indicated out-of-body experiences at the onset/offset of sleep.⁶

• Of the people reporting sleep-related hallucinations, 54.6% also had day-time hallucinations. ⁴

• A further recent study reported a prevalence of 18% in the general population without any neuropsychiatric disorder. ⁷

• Narcolepsy is typically associated with both hypnagogic and hypnopompic hallucinations, alongside excessive daytime sleepiness, cataplexy, sleep paralysis, and disrupted nocturnal sleep.⁸

• There is a tendency for hypnagogic and hypnopompic hallucinations associated with narcolepsy to be associated with certain HLA phenotypes.⁹

• Patients with Parkinson's disease are more likely to report sleep-related hallucinations, with the prevalence at 45%. ⁷

• Antidepressants have been reported to be associated with hypnagogic and hypnopompic hallucinations. Both SSRIs and tricyclics have been implicated.¹⁰

• Other conditions associated with an increased incidence of sleep-related hallucinations include isolated sleep paralysis, migraine, sensory deprivation, Charles Bonnet syndrome, and preclinical psychosis.⁷

• Hospital admission may precipitate sleep-related hallucinations in those who have not previously experienced them. ¹¹¹²

• Hypnagogic hallucinations occur at the onset of sleep, either by day or at night.

• Hypnopompic hallucinations occur on waking.

• Visual hallucinations usually consist of simple forms such as coloured circles or parts of objects that may be constant or changing in size. A formed image of an animal or a person may appear and it is often in colour.

• Auditory hallucinations can range from a few sounds to an elaborate melody. Speech is also reported.

• Another type of hallucination that is sometimes reported at the onset of sleep involves elementary cenesthopathic feelings (such as experiencing picking, rubbing, or light touching), changes in location of body parts (such as an arm or a leg), or feelings of levitation or extracorporeal experiences (like moving the body in space or floating above the bed) that may be quite elaborate.

• Alice in Wonderland syndrome has been reported to occur more commonly in hypnagogic states. ¹³

• Musical release hallucinations are complex auditory phenomena, affecting mostly the deaf elderly population, in which individuals hear vocal or instrumental music.

There are usually no abnormal physical signs.

• Narcolepsy.

• Schizophrenia can cause hallucinations, including derogatory auditory remarks.

• There may be drug misuse.

• Sleep terrors in children.

• Focal seizures.

• Absence seizures.

• Blood tests and imaging are likely to be normal.

• Referral to a special sleep laboratory may be required to diagnose narcolepsy.¹⁴

• Treatment is not necessarily required. Sleep-related hallucinations are common and do not need any management if they are not causing distress. Reassurance may alleviate such distress.

• Following a regular sleep schedule, ensuring enough sleep, and avoiding drugs and alcohol may help. ¹⁵

• Good sleep hygiene includes removing electronic devices from the bedroom, avoiding large meals before bedtime and avoiding caffeine and alcohol before bedtime.

• There is little evidence for management of hypnagogic or hypnopompic hallucinations specifically. SSRIs are sometimes used for this although there is also evidence that they can cause sleep-related hallucinations.

• Hypnagogic hallucinations associated with narcolepsy can be treated with REM-suppressing antidepressants, such as venlafaxine (Effexor®) or other selective serotonin reuptake inhibitors. ^{14 16}

• Sodium oxybate is as effective as modafinil and pitolisant as treatment for narcolepsy but it should not be combined with other CNS depressants or alcohol.¹⁷ Sodium oxybate is also known as GHB, a known street drug of abuse.

• Pitolisant, an H3 receptor antagonist, and solriamfetol, a dopamine and noradrenaline reuptake inhibitor, are the most recently approved treatments for narcolepsy in the European Union (pitolisant) and the USA (pitolisant and solriamfetol).¹⁸

• These medications are generally not available for prescribing within general practice and are specialist-only medications.

For the treatment of narcolepsy, see the separate Narcolepsy and cataplexy article.

If the patient has narcolepsy the prognosis is as for that disease.¹⁹ If not, reassurance is all that is required.

• Salvador Dali used his visual hypnagogic hallucinations to influence his art.²⁰

• Carl Jung described many examples of hypnagogic hallucinations and, at times, struggled to distinguish these from reality. ²¹

• Some scientists report hypnagogic hallucinations helping with specific conundrums. ²²

• Visual hypnagogic hallucinations are thought to be behind some of the historic legends around ghost stories and night demons. ²³²⁴