What is a hallucination?

Hallucinations are things that appear to be real to a person, but in fact, are not real. Hallucinations may take different forms, including:

• seeing people or objects that are not there
• hearing voices of people who are not present. The voices may talk directly to the person having the hallucination, or may be multiple voices talking to each other inside the person's head.
• smelling odors, either pleasant or bad, that no one else detects
• feeling sensations, such as bugs crawling on your skin when there are no insects present, or someone touching you when no one else is there

Hallucinations may have many different causes, including use of certain drugs (such as LSD or marijuana), certain medical conditions (such as epilepsy, narcolepsy, high fevers, Alzheimer's disease, brain cancer or severe liver or kidney disease), certain mental disorders (such as schizophrenia, dementia, or psychotic depression--especially when hallucinations comment on the patient or command the patient), prolonged sleep deprivation and certain sensory disorders, such as blindness or deafness. 

A hallucination is the perception of something being present that is not. Hallucinations can take the form of hearing, seeing, tasting, or smelling things that are not actually there. This can be a sign of a mental illness. If you believe you are having hallucinations, you should be evaluated by a trained medical professional.