Oneirism or delirium of sleep is an alteration of consciousness that is often caused by the abuse of psychoactive substances or organic brain disorders such as epilepsy and parasomnias. Its main characteristic is the appearance of hallucinations similar to those that occur when we dream, but in this case they occur in the waking state.

In this article we will describe the characteristics, symptoms and main causes of oneirism . In order to do so, it is necessary to look at other concepts and disorders associated with sleep deliriums, such as “productive consciousness disorder”, “parasomnia” or the very term “hallucination”.

What is oneirism or delirium of sleep?

Oneirism, also known as sleep delirium, is a psychological state characterized by the presence of hallucinations similar to those that occur during dreams but which occur during wakefulness. Both nomenclatures refer to this fact, since the Greek word “oneiros” can be translated as “dream” or “reverie”.

This phenomenon is associated with the abuse of certain substances, such as toxic products or alcohol and other drugs, as well as with physiopathological alterations of the brain. However, on other occasions, oneirism does not have a pathological component, but can also be the result of normal biological factors, such as sleep deprivation.

Sleep delirium is part of the group of disorders that we know as “productive disorders of consciousness”, which also includes delirium (very common in elderly people in hospital and in alcoholics with withdrawal syndrome), depersonalization, de-realization or phantom limb syndrome.

The common aspect that unites this group of disorders is that in all of them hallucinations appear due to alterations that affect consciousness. We talk about hallucination when a person perceives something through any sensory channel (auditory, visual, etc.) without there being a stimulus that justifies it, especially if he or she believes that such perception is real.

Main symptoms and manifestations

In the case of oneirism, and as tends to happen when there are organic alterations of the brain present or when substances with psychoactive effects are consumed, the hallucinations are mainly of a visual nature . However, sometimes tactile hallucinations and to a lesser extent auditory, olfactory and taste hallucinations are also identified.

Hallucinations do not always occur in a single sensory mode, but can be multimodal; for example, hearing a threatening voice and feeling someone’s breath in your ear would be a multimodal hallucination. Some authors use the concept of “sleep delirium” only when the hallucinations are of this type, while “oneiric” would be a broader term.

Like most productive disorders of consciousness, oneiricism is often associated with the loss of contact with reality, either completely or partially . Sometimes the person may lose consciousness of himself or herself or perceive the environment in which he or she is in a hallucinatory way.

Most often, sleep deliriums are of a transitory nature, closely related to specific biological factors, and do not have a significant impact on the long-term psychological state of the sufferer. Another characteristic of oneirism is that it usually begins suddenly, in a matter of hours or at most days.

Causes of sleep delusions

Oneirism arises as a consequence of different organic factors that affect the brain . The most common is intoxication due to the abuse of certain substances, but any transitory or chronic brain disorder has the potential to cause these symptoms, especially those that affect the processes related to wakefulness and sleep.

1. Abuse of Psychoactive Substances

The most common cause of sleep delusions is excessive consumption of alcohol, antidepressant and sedative-hypnotic drugs (especially barbiturates) and drugs with hallucinogenic effects, including hallucinogenic mushrooms or psilocybin, mescaline, which is found in peyote, and lysergic acid or LSD.

Poisoning from certain types of poisons and other substances that are toxic to the human body is also associated with the occurrence of dreamlike episodes.

2. Parasomnias

Parasomnias are a group of sleep disorders characterized by the appearance of abnormal behaviors, perceptions or emotions in the transition periods between sleep and wakefulness. Oneirism is especially common in REM sleep disorders , during which dreams are very vivid and muscle tone is elevated.

3. Organic alterations

Epilepsy, in which there are episodes of abnormal brain activity that often cause seizures, is one of the chronic organic disorders most closely related to delirium of sleep. Other relevant organic processes include febrile states, infections, gastrointestinal haemorrhages and degenerative brain diseases .

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4. Non-pathological factors

People without relevant organic disorders and who are not under the effect of a substance we have mentioned may also have low-intensity dreamlike delusions. Among the non-pathological factors that predispose to oneiric disorder are intense fatigue, sleep deprivation, indigestion and states of marked anxiety.