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). The phenomenon is thought to have been first described by the Dutch physician Isbrand Van Diemerbroeck in 1664.¹ The person may hear sounds that are not there and see visual hallucinations. These visual and auditory images are very vivid and may be bizarre or disturbing.

Usually it is part of the tetrad of narcolepsy that includes:

• Excessive daytime sleepiness
• Cataplexy
• Hypnagogic hallucinations
• Sleep paralysis.

This tetrad is rarely seen in children.

For further details, see our article on Narcolepsy.

• Hypnagogic hallucinations can occur without narcolepsy. People may be reluctant to admit to them for fear of being thought mentally ill.
• Sex ratio is equal.
• A telephone interview of nearly 5,000 people aged 15 to 100 in the UK² showed that 37% of the sample reported experiencing hypnagogic hallucinations and 12.5% reported hypnopompic hallucinations. Both types of hallucinations were significantly more common among subjects with symptoms of insomnia, excessive daytime sleepiness or mental disorders. Hypnagogic and hypnopompic hallucinations were much more common than expected, with a prevalence that far exceeds that which can be explained by the association with narcolepsy. Hypnopompic hallucinations may be a better indicator of narcolepsy than hypnagogic hallucinations in subjects reporting excessive daytime sleepiness.

• There is a tendency for it to be associated with certain HLA phenotypes.
• Prazosin, an alpha1-antagonist, worsens symptoms.

• Hypnagogic hallucinations can occur at the onset of sleep, either by day or at night. They are usually quite vivid and visual.
• 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 are common but other senses are seldom involved. Auditory hallucinations can range from a few sounds to an elaborate melody. Threats or criticism are 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.
• There may be a history of narcolepsy with the ability to fall asleep if at all tired or bored, often with social embarrassment. It may lead to the inability to hold down a job.

See our dedicated article on Cataplexy.

There are usually no abnormal physical signs.

• It is important to decide if this is narcolepsy as it is a treatable condition.
• Schizophrenia can cause hallucinations including derogatory auditory remarks. In people who experience hypnogogic or hypnopompic images but do not have narcolepsy, the tendency towards psychosis is greater than in others.³
• Musical release hallucinations are complex auditory phenomena, affecting mostly the deaf elderly population, in which individuals hear vocal or instrumental music. Progressive hearing loss from otosclerosis disrupts the usual external sensory stimuli necessary to inhibit the emergence of memory traces within the brain, thereby "releasing" previously recorded perceptions.
• There may be drug abuse.
• Sleep terrors in children.
• Partial seizures.
• Absence seizures.

• Blood tests and imaging are likely to be normal.
• Referral to a special sleep laboratory may be required to diagnose narcolepsy.

• Tricyclic antidepressants hold back the dreaming state and may be beneficial. However, a Cochrane review was unimpressed by the evidence.⁴
• Musical hallucinations may be helped by the atypical antipsychotic quetiapine.⁵

See the dedicated article for the treatment of narcolepsy.

If the patient has narcolepsy the prognosis is as for that disease. If not, reassurance is all that is required. If it is disturbing, tricyclic antidepressants may be used intermittently.