Hallucinations during sleep are a phenomenon that can target any sensory perception, be it visual, auditory, tactile, olfactory, or other. Sleep hallucinations are often confused with both illusions and dreams. They occur in the state between waking and sleeping, although the person is considered to be technically asleep during these hallucinations. This is in contrast to dreams or lucid dreams, which occur while the person is asleep.

What’s the Difference Between Illusions and Hallucinations?

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. Hallucinations most often occur in the stages before or after sleep, explaining their connection as a sleep-related phenomenon. Hallucinations can occur at any time, though this article will only look at hallucinations as they are connected to sleep. Hallucinations are common, most notably sleep-related hallucinations, with over 10 percent of the population experiencing one at some point in their life.

Hypnagogic Hallucinations, Hypnopompic Hallucinations, and Sleep Paralysis

The two forms of sleep related hallucinations are called hypnagogic (hypnagogia) and hypnopompic (hypnopompia) hallucinations. Hypnagogic hallucinations occur just before sleep, and may be accompanied by sleep paralysis, a state in which the subject is physically immobile but fully conscious. Hypnopompia, which is often considered as part of a dream by the subject, also involves difficulty breathing and muscle tightness. Hypnopompia occurs upon waking, and may also be accompanied by sleep paralysis.

Sleep paralysis is much more common in hypnopompia than in hypnagogia. Sleep paralysis is often confused by the person experiencing it as part of a lucid dream, which accounts for the high number of recalled dreams with elements of being frozen in place or being unable to move. Common hypnopompic experiences include the sensation of falling and the feeling of a presence in the room.

Distinguishing Dreams From Sleep Hallucinations

Sleep hallucinations can cause confusion, as they will often be indistinguishable from reality in your mind. In contrast, upon waking from a dream during REM sleep, most people will clearly recognize it was a dream they were experiencing, or may immediately forget about the dream entirely upon waking. Hallucinations may also cause fear, especially upon waking, as they may include clear and complex visual images that are distorted or make no sense.

Sleep-related hallucinations can occur in as many as 25 percent of people, as opposed to under 5 percent for non sleep-related hallucinations. They are most commonly found in young adults and teens, and the frequency of hallucinations seems to decrease with age. Females are more likely to experience them than males.

Known Causes and Treatment of Sleep-Related Hallucinations

Sleep-related hallucinations may be a direct result of alcohol or drug use, or could be due to insomnia, anxiety, stress or other factors. People with narcolepsy have a high rate of sleep hallucination occurrences.

Sleep hallucinations may not need treatment, as they often occur infrequently and do not affect sleep quality. They may be a sign of mental stress though, or if coupled with daytime sleepiness, even narcolepsy. If the hallucinations are causing fear or anxiety, or to validate its causes, you may want to talk to your doctor or a sleep specialist. When issues of mental stress are suspected, you may be advised to contact a therapist, or practice relaxation techniques before bedtime to help the mind shut down. It may also be advised to stay out of bed until feeling extremely tired, to avoid lying awake in bed and having the mind wander onto issues that may be causing you stress or anxiety. It has been shown in studies that the clearer a person’s mind is, the less likely they are to hallucinate, or even dream.

If the hallucinations are the result of medication, drug or alcohol use, it may be advised to refrain from their use, and you may need to change medications if this is the case.

Any suspected case of narcolepsy should be consulted with a sleep specialist, and an overnight sleep study performed to look into it further. Narcolepsy can be a debilitating disorder that can be treated.