Hallucinations often involve seeing things that aren't there.
Hallucinations are perceptions of the mind without a causative external stimulus from the real world; in other words, they are things we hear, see, smell or otherwise sense even though they are not there. Seeing visions, hearing voices, music or other sounds and experiencing tactile sensations such as "crawling skin" are all hallucinations. Hallucinations have a wide variety of causes.
Drugs
Hallucinations are often caused by psychoactive drugs or compounds known as hallucinogens. Psychedelics such as LSD or psilocybin mushrooms are known to produce hallucinations. They affect the brain's levels of serotonin and other neurotransmitters. Users of dissociative drugs, such as ketamine, also frequently hallucinate. Deliriants such as jimson weed also cause full-scale hallucinations. These drugs most often cause acute visual or auditory hallucinations. Hospital patients sometimes hallucinate from the effects of anesthetic drugs. Certain prescription drugs, including amphetamines and barbiturates, may also cause hallucinations.
Schizophrenia
One of the most common symptoms of paranoid schizophrenia is auditory hallucinations. Schizophrenic people often hear voices that begin as whispers or mumblings but gradually become clearer and more audible. The sufferer does not realize the voices are coming from inside his head, and he may imagine people are talking about him behind his back. Sometimes the voices command the schizophrenic to commit violent acts or other things they would not normally do.
Charles Bonnet Syndrome
Charles Bonnet Syndrome is a condition where people who are losing their vision to glaucoma or other conditions begin to experience visual hallucinations. People with CBS are usually aware that their hallucinations are not real; their perceptions are not associated with mental health imbalances and delusions. CBS hallucinations may take the form of simple, brightly colored repeating patterns that appear to be superimposed over the real world. More complex, complicated and highly detailed visions of people, places or animals may also be seen. CBS hallucinations are temporary and usually subside after a year or so.
Other Hallucinations
A person who begins to hallucinate for no apparent reason should seek medical care. The hallucinations may cause anxiety, nervousness or fear. Sometimes they are symptoms of medical conditions such as Alzheimer's, epilepsy, migraine episodes or drug withdrawals that may require treatment. Hypnagogic or hypnopompic hallucinations occur just before falling asleep or awakening and are harmless.
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