Delirium is a medical term used to describe a mental state. There are several definitions (including those in the DSM-IV and ICD-10). However, all include some core features.
intrusive abnormalities of awareness and affect, such as hallucinations or innappropriate emotional states.
Delirium should be distinguished from psychosis, in which consciousness and cognition may not be impaired, and dementia which describes an acquired intellectual impairment usually resulting from a degenerative brain disease.
Delirium may be caused by severe physical or mental illness. Fever, poisons (including toxic drug reactions), brain injury, surgery, severe lack of food or water, drug and severe alcohol withdrawal are all known to cause delirium.
It is also referred to as 'acute confusional state' or 'acute brain syndrome'.
Hallucinations (perceived sensory experience with the lack of an external source) or distortions of reality may occur in delirium. Commonly these are visual distortions, and can take the form of masses of small crawling creatures (particularly common in delirium tremens, caused by severe alcohol withdrawal) or distortions in size or intensity of the surrounding environment.
Strange beliefs may also be held during a delirious state, but these are not considered delusions in the clinical sense as they are considered too short lived. Interestingly, in some cases sufferers may be left with false or delusional memories after delirium, basing their memories on the confused thinking or sensory distortion which occurred.
Abnormalities of affect include any distortions to perceived or communicated emotional states. Emotional states may also fluctate, so a person may rapidly change between, for example, terror, sadness and jocularity.
