What are hallucinations? Hallucinations are sensations or perceptions that occur in a wakeful state and seem real, but are created by the brain. Hallucinations may be seen, heard, smelled, felt or tasted. They can be pleasant or threatening and may be related to sensations, imagery, or events of the past, or they may be unrelated to experiences. Common hallucinations include hearing voices; seeing objects, lights or people who are not there; and the sensation of crawling skin. Hallucinations are different than delusions, vision changes, and dreams. Delusions are related to thought processes and conclusions. Vision changes, such as floaters, spots, and flashes of light, can be caused by conditions of your eye. Dreams occur while you are asleep. Hallucinations are associated with some psychiatric disorders or medical conditions. Auditory hallucinations are most common. Psychiatric conditions associated with hallucinations include schizophrenia, schizoid and schizotypal personality disorders, psychotic depression, and bipolar disorder. Medical conditions affecting the central nervous system, such as brain tumors, delirium, dementia, epilepsy and other seizure disorders, and stroke, can be associated with hallucinations. Hallucinations can also be experienced with high fevers. Some people abuse certain medications and substances because those items can cause hallucinations. Other substances, such as alcohol, can cause hallucinations when used in large quantities or during withdrawal. Hallucinations can be side effects of some medications and may occur with visual or hearing loss. Sleep deprivation or severe fatigue can also cause hallucinations. Hallucinations can be symptoms of serious and even life-threatening conditions. Seek immediate medical care (call 911) if you, or someone you are with, experience hallucinations that cannot be distinguished from reality, or that are accompanied by bluish coloration of the lips or fingernails; chest pain or pressure; cold, clammy or dry, hot skin; confusion or loss of consciousness for even a moment; high fever (higher than 101 degrees Fahrenheit); persistent vomiting; rapid, slow or absent pulse; respiratory or breathing problems, such as rapid or slow breathing, shortness of breath, or no breathing; seizure; serious injury; severe abdominal pain; or threatening, irrational or suicidal behavior. Seek prompt medical care if you are being treated for a condition that causes hallucinations and your symptoms are persistent, worsen, or otherwise cause you concern.