Hypnagogic Hallucinations Causes, Symptoms, and Treatment

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). 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^[2]:

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

This tetrad is rarely seen in children.

See the separate Narcolepsy and Cataplexy article.

How common are hypnagogic hallucinations? (Epidemiology)^[3]

• Hypnagogic hallucinations can occur without narcolepsy. People may be reluctant to admit to them for fear of being thought mentally ill. However, they are thought to occur in most people at least once in their lives.
• A UK study had 37% of the sample reported experiencing hypnagogic hallucinations, and 12.5% reported hypnopompic hallucinations^[4]. Both types of hallucinations were significantly more common among subjects with symptoms of insomnia, excessive daytime sleepiness or mental disorders. 
• A recent study had a prevalence for hallucinations in the auditory domain (the least common type) at 6.8%, whereas 12.3% reported multimodal hallucinations, and 32.2% indicated out-of-body experiences at the onset/offset of sleep^[5].
• Group comparisons of hallucinations in the auditory modality showed that individuals who experienced only auditory hallucinations scored significantly (p <0.05) lower than those who also experienced daytime auditory hallucinations on a range of variables including mental health, anxiety, childhood happiness, and well-being.

Risk factors for hypnagogic hallucinations

• There is a tendency for hypnagogic and hypnopompic hallucinations associated with narcolepsy to be associated with certain HLA phenotypes^[6].
• Tricyclic antidepressants have been reported to be associated with hypnagogic and hypnopompic hallucinations^[7].

Hypnagogic hallucinations symptoms

Narcolepsy is often under-diagnosed and delays of 5-10 years are common before making a firm diagnosis^[8]. Close to 50% of patients develop symptoms in their teenage years:

• 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.

Signs

There are usually no abnormal physical signs.

Differential diagnosis

• It is important to decide if this is narcolepsy, as it is a treatable condition.
• Schizophrenia can cause hallucinations, including derogatory auditory remarks.
• 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 misuse.
• Sleep terrors in children.
• Focal seizures.
• Absence seizures.

Investigations

• Blood tests and imaging are likely to be normal.
• Referral to a special sleep laboratory may be required to diagnose narcolepsy^[2].

Hypnagogic hallucinations treatment and management

• Hypnagogic hallucinations can be treated with REM-suppressing antidepressants, such as venlafaxine (Effexor®) or other selective serotonin reuptake inhibitors^{[9, 2]}.
• Fluoxetine has also been recommended for this indication^[10].
• Musical hallucinations may be helped by olanzapine, quetiapine, fluvoxamine, clomipramine, carbamazepine, valproate and donepezil^[11].
• Sodium oxybate is as effective as modafinil and pitolisant as treatment for cataplexy but it should not be combined with other CNS depressants or alcohol^[12]. 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 EDS associated with narcolepsy in the European Union (pitolisant) and the USA (pitolisant and solriamfetol)^[13]. 

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

Prognosis

If the patient has narcolepsy the prognosis is as for that disease^[8]. If not, reassurance is all that is required. If it disturbs the patient, medication may be used intermittently.