Oneiroid syndrome

Oneiroid syndrome (OS) is a psychiatric condition marked by dream-like disturbances of consciousness. It is characterised by vivid scenic hallucinations, catatonic symptoms (ranging from stupor to agitation), delusions, and kaleidoscopic psychopathological experiences. The term originates from the Ancient Greek words "ὄνειρος" (óneiros, meaning "dream") and "εἶδος" (eîdos, meaning "form" or "likeness"), translating to "dream-like" or "oneiric" (occasionally described as "nightmare-like").

The oneiroid state is a hallmark of this syndrome, defined by an altered state of consciousness where individuals experience profound confusion and disorientation regarding time and place. Patients may be entirely immersed in their hallucinatory experiences, often showing little to no engagement with external reality. This phenomenon is sometimes referred to as oneiroid schizophrenia, particularly when associated with catatonic symptoms and hallucinatory absorption.

In oneiroid syndrome, the dream-like experiences are vivid to the point of being perceived as real by the individual. However, unlike delirium, the imaginative experiences in OS are internally projected—patients perceive them as originating within their minds rather than as external phenomena.

Potential causes include:

• Endogenous conditions, such as schizophrenia, particularly catatonic subtype.
• Exogenous factors, including infectious diseases (e.g., encephalitis), intoxication (e.g., hallucinogenic substances), and traumatic brain injuries.

Despite its distinct clinical presentation, oneiroid syndrome is not widely recognised in contemporary psychiatric diagnostic systems such as the DSM-5. Its absence from standard classification systems likely contributes to its limited coverage in psychiatric textbooks.