What are hallucinations?

A hallucination occurs when environmental, emotional, or physical factors such as stress, medication, extreme fatigue, or mental illness cause the mechanism within the brain that helps to distinguish conscious perceptions from internal, memory-based perceptions to misfire. As a result, hallucinations occur during periods of consciousness. They can appear in the form of visions, voices or sounds, tactile feelings (known as haptic hallucinations), smells, or tastes.

Patients suffering from dementia and psychotic disorders such as schizophrenia frequently experience hallucinations. Hallucinations can also occur in patients who are not mentally ill as a result of stress overload or exhaustion, or may be intentionally induced through the use of drugs, meditation, or sensory deprivation. A 1996 report, published in the British Journal of Psychiatry, noted that 37% of 4,972 people surveyed experienced hypnagogic hallucinations (hallucinations that occur as a person is falling to sleep). Hypnopomic hallucinations (hallucinations that occur just upon waking) were reported by 12% of the sample.

Illusions are different from hallucinations. Illusions involve misinterpreting something that is real. Everyone experiences illusions at some time. They are generally not a cause for concern. People with only partial vision or partial hearing often experience illusions. This is because human brains have a natural tendency to fill in missing gaps. For instance, it is not unusual for elderly people to mistake the hum of an air conditioner for the murmur of voices.

More information on hallucinations