What is Hallucination?
[[File:The Temptation of Saint Anthony (Grünewald) detail.jpg|thumb|The Temptation of Saint Anthony, Detail, [[Mathias Grünewald]], 1515. This painting might have been influenced by the description of hallucinations.]] A '''hallucination''' is seeing, hearing, tasting, smelling or feeling things that do not really exist. Usually, people have to be [[awake]] and [[conscious]] to have hallucinations. That way, a person who sees or hears something that is not really there has a hallucination. Hallucinations are different from [[dream]]s. When people dream, they are not awake. Hallucinations are also different from [[illusion]]s. Illusions are based on real perceptions, which are distorted or interpreted in a wrong way. Certain drugs can cause hallucinations. Some [[illegal drug]]s are taken because they cause hallucinations. Certain [[mental illness]]es can also cause hallucinations. In some cases, withdrawal of a drug can also cause hallucinations. This has especially been reported by people trying to stop taking [[sleeping pill]]s, or by [[alcoholic]]s. People who have hallucinations are not necessarily ill, lack of [[sleep]] can also cause hallucinations. Hallucinations just before going to sleep or just after waking up are considered normal. == Types of hallucinations == Hallucinations can affect all of a person's [[Sensory system|senses]]. People with the mental illness of [[schizophrenia]] may hear [[Auditory hallucination|sounds or voices]] that are not really there. People with certain mental illnesses may also have hallucinations in which they see a person or thing which is not really there. People are less likely to have hallucinations in which they smell or touch something that is not really there. Certain forms of [[epilepsy]] can cause hallucinations. Finally, hallucinations can be the result of certain substances taken or of certain physical constellations. Most of the time, these substances are taken to get the hallucinations. Sometimes, (severe) lack of [[sleep]], or high [[fever]] can lead to