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 dreams. When people dream they are not awake. Hallucinations are also different from illusions. Illusions are based on real perceptions, which are distorted or interpreted in a wrong way.