What really happens in the brain during a hallucination?

A hallucination occurs when you perceive a sight, sound, smell, touch, or taste that is not actually present.  Hallucinations are often a symptom of psychosis-related mental disorders such as schizophrenia, but they can also occur with substance use and neurological conditions, like epilepsy.  The exact mechanism is still not completely understood but may involve chemical disruptions that interfere with the brain’s ability to interpret information from the outside world.