Hallucinations, with the exception of religious experiences, are usually abnormal as the circumstances causing them are usually abnormal. Such circumstances include changes in the brain related to electrolyte disturbances, high fevers, liver or kidney failure or certain drugs. Illusions, however, may be normal as the circumstances causing them may be normal. Such circumstances include poor lighting or, paradoxically, bright sunlight. Such hallucinations can usually be ignored.
Hallucinations can also be frightening.
Such hallucinations must be treated. Aside from the terror they instill in the patient, and the spouse or caregiver, such hallucinations may, in time, be followed by confusion, delusions, paranoia, and psychosis. Hallucinations are invariably preceded by sleep disturbances. Sleep disturbances include difficulty falling asleep, multiple awakenings from sleep, crying-out during sleep, and vivid dreams. A study conducted in Chicago examined the relationship between sleep disturbances and hallucinations.