What Is the Definition of Hypnagogic Hallucinations?

The role of sleep in these sensations

Mature woman sleeping in bedroom. Credit: Tetra Images / Getty Images

What is the definition of a hypnagogic hallucination? Learn more about these sensations and their connection to sleep with this overview.

What Does a Hypnagogic Hallucination Feel Like?

A hypnagogic hallucination is a vivid, dream-like sensation that an individual hears, sees, feels or even smells and that occurs near the onset of sleep. As the individual falls asleep, for example, he experiences intense hypnagogic hallucinations and imagines that there are other people in his room.

These episodes are usually brief and may also occur as someone transitions from slumber to wakefulness (hypnopompia). 

"Illusions occur while awake, and are classified as a sensory misrepresentation of an external stimulus, while hallucinations occur in the absence of any external stimuli," according to the American Sleep Association.

The ASA has determined that these hallucinations are common, with at least 10 percent of the population experiencing such sensations. Teens, young adults and girls and women are most likely to have these hallucinations.

Sometimes, hypnagogic hallucinations can signal a problem. Medication, illegal drug use, alcohol and anxiety can all give rise to these hallucinations. They are also one of the four cardinal symptoms of the sleep disorder narcolepsy.

What Is Narcolepsy?

A neurological disorder, narcolepsy occurs when the brain fails to effectively regulate sleep-wake cycles.

Narcolepsy can lead to a person feeling excessively sleepy during the day. The narcoleptic may give in to the irresistible urge to fall asleep during typical waking hours. Accordingly, narcolepsy is also referred to as "excessive uncontrollable daytime sleepiness."

The disorder has been portrayed in films such as director Gus Van Sant's "My Own Private Idaho," starring Keanu Reeves and the late River Phoenix, who played a narcoleptic in the 1991 movie.

In such films, narcoleptics are portrayed as people who simply pass out during the day--in the middle of the street, for example. The disorder isn't so dramatic in real life but it can be debilitating. It is also rare, with fewer than 200,000 cases occurring in the U.S. population per year. Narcolepsy may last for a short time in a person's life or for years.

Hypnagogia and Sleep Paralysis

Oftentimes hypnagogic hallucinations and sleep paralysis go hand in hand. During sleep paralysis a person is immobile, unable to move, despite being conscious. This state occurs when people are transitioning between sleep and wakefulness and can cause an individual to be fearful.

It may be difficult for the person to realize the paralysis is fleeting. During a sleep paralysis episode, a person may struggle to breath or feel muscle tightness. Sleep paralysis most often occurs when a person is waking up from sleep (hypnopompia) than when person is drifting off to sleep (hypnagogia). 

Taking Action

If you think you're suffering from hypnagogic hallucinations or your loved ones think you are, talk to your doctor about the potential causes for these episodes.

You may need to be referred to a sleep specialist or observed for further evaluation. If these hallucinations don't appear to be causing major disruptions to your life or sleep cycle, no further action may be taken.

However, it may be wise for you and your loved ones to familiarize yourselves with these hallucinations, so that you all feel a greater sense of control over them when they do occur.

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