Hypnagogic hallucinations are imagined sensations that seem very real. They occur as a person is falling asleep, and are also referred to as sleep hallucinations.

The term hypnopompic describes the period when a person wakes up. Hypnagogic defines the period when a person falls asleep.

A hallucination is anything that can be sensed but is not real. A hallucinated smell, taste, vision, or sound is only experienced in a person’s mind and not by others.

Hallucinations that occur around sleep have fascinated scientists, writers, and philosophers for many centuries. Research about their causes and link to dreams is ongoing.

Aside from narcolepsy, hypnagogic hallucinations may be caused by Parkinson’s disease or schizophrenia.

Sleepwalking, nightmares, sleep paralysis, and similar experiences are known as parasomnia. Often there is no known cause, but parasomnia can run in families.

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People may have vivid hallucinations while falling aseep.

A person will experience vivid hallucinations as they fall asleep, or just before falling asleep. These can be images, smells, tastes, tactile sensations, or sounds.

A person may also feel as if they are moving while their body is still.

This sensation could be a feeling of falling or flying.

Visual hallucinations

The most common hypnagogic hallucinations are visual. They may include images of people, animals, or moving objects.

Images can be quite complex and detailed, and may not make any sense.

Other symptoms

During a hypnagogic hallucination, a person knows that they are awake. The images, sounds, or other sensations may last a number of minutes. They may prevent a person from falling asleep.

These hallucinations may happen at the same time as sleep paralysis.

Difference from dreaming

The key difference between a dream and a hypnagogic hallucination is that the hallucination will feel very real. A person may feel sure that they have seen or felt something, and this can be frightening or confusing.

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Consuming alcohol may increase the risk of hypnagogic hallucinations.

Certain factors may increase the likelihood of experiencing a hypnagogic hallucination.

They tend to occur less frequently as a person ages, and women are more likely to experience these hallucinations than men.

If a person uses drugs or alcohol, they may be more likely to experience hypnagogic hallucinations. The condition is also linked to anxiety and insomnia.

Hypnagogic hallucinations are not usually a risk to health.

Certain medical conditions are associated with these hallucinations. If a person has any of the following symptoms, they may wish to see a doctor.

  • Symptoms of narcolepsy: These include muscle weakness, being very sleepy during the day, and having a disturbed sleep at night.
  • Symptoms of schizophrenia: These include hearing voices, having confused thoughts, and experiencing changes in behavior.
  • Symptoms of Parkinson’s disease: These include slow movement, muscle stiffness, and shaking in the hands and other parts of the body.

A migraine may also lead a person to see colors, lights, or images that do not exist. These visualizations are called auras. They usually occur alongside a headache and are different from hallucinations.

Hypnagogic hallucinations can be very disturbing. They can stop a person from sleeping well, and cause stress or anxiety. If this is the case, a person may wish to see a doctor.

If a person feels that they can live with their hypnagogic hallucinations, they may not need treatment. If there is no underlying medical condition, changes to lifestyle may lessen the frequency of hallucinations.

Getting enough sleep and avoiding drugs and alcohol can reduce their frequency. If hypnagogic hallucinations cause disrupted sleep or anxiety, a doctor might prescribe medication.

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A doctor may be able to provide advice if hypnagogic hallucinations are affecting well-being.

When these hallucinations are not caused by an underlying condition, they usually do not have long-term complications. Their most common effects are disturbed sleep, and stress or anxiety.

However, hypnagogic hallucinations can cause a person to wake in terror and scream or shout, which may disturb a partner or roommate.

Also, a person experiencing a hallucination may fall out of bed or otherwise injure themselves.

Many of these issues can harm health and well-being. A person may wish to consult a doctor for advice or treatment.

During sleep, many parts of the brain are still active. Processes such as breathing and circulation are normal.

Most people will also dream, although not everyone can remember doing so. The reasons for dreaming are still not completely understood. It may be a way for the brain to sort through information or recall memories.

The body will cycle through periods of deeper and lighter sleep throughout the night. Dreaming and types of parasomnia, such as sleepwalking, mostly happen during deeper sleep.

As a person falls asleep or wakes up, they will usually enter a period of lighter sleep. Narcolepsy can cause a person to enter directly into a period of deeper sleep, or wake up in the middle of one. This may cause dreams or hallucinations to feel more real.

Scientists are not sure what causes hypnagogic hallucinations in people who do not have narcolepsy. It may happen for similar reasons, as periods of deeper and lighter sleep overlap.

Hypnagogic hallucinations tend to have no long-term side effects. They often happen because of an underlying medical condition or during periods of poor sleep and stress.

Getting advice and treatment for an underlying condition can help to reduce the frequency of hypnagogic hallucinations.

Making changes to a sleep schedule and getting more rest will often resolve the condition.