A hallucination occurs when environmental, emotional, or physical factors such as stress, medication, extreme fatigue, or mental illness cause the mechanism within the brain that helps to distinguish conscious perceptions from internal, memory-based perceptions to misfire. As a result, hallucinations occur during periods of consciousness. They can appear in the form of visions, voices or sounds, tactile feelings (known as haptic hallucinations), smells, or tastes.

Hallucinations are abnormal sensory perceptions that occur while a person is awake and conscious and are unrelated to outside events; in other words, seeing or hearing things that aren't there.

If the hallucination doesn’t cause problems for you, the person or other family members, you may want to ignore it. However, if they happen continuously, consult a physician to determine if there is an underlying physical cause. Also, have the person’s eyesight and hearing checked, and make sure the person wears his or her glasses and hearing aid on a regular basis.

Signs and symptoms of Hallucination

Rigid muscles. Muscle stiffness (rigidity) often occurs in your limbs and neck. Sometimes the stiffness can be so severe that it limits the size of your movements and causes pain.

“behavioral and psychiatric symptoms” describes a large group of additional symptoms that occur to at least some degree in many, but by no means all, individuals with Alzheimer’s.

When just falling asleep or, less often, when awakening, the person may clearly see images or hear sounds that are not there. These extremely vivid hallucinations (called hypnagogic hallucinations) are similar to those of normal dreaming but are more intense.

Impaired balance. Your posture may become unstable as a result of Parkinson's disease. Often this problem remains minor for many years.

Schizophrenia ranges from mild to severe. Some people may be able to function well in daily life, while others need specialized, intensive care. In some cases, schizophrenia symptoms seem to appear suddenly. Other times, schizophrenia symptoms seem to develop gradually over months, and they may not be noticeable at first.

Causes of Hallucination

Drugs: Use of Psychotomimetics and Medications side-effects: Hallucinogenics such as ecstasy, LSD, mescaline (3,4,5-trimethoxyphenethylamine, or peyote), and psilocybin trigger hallucinations. Other drugs such as marijuana and PCP have hallucinatory effects. Certain prescription medications may also cause hallucinations. In addition, drug withdrawal may induce tactile and visual hallucinations.

Mental illness. Up to 75% of schizophrenic patients admitted for treatment report hallucinations.

Intoxication or withdrawal from such drugs as marijuana , LSD , cocaine or crack, heroin, and alcohol.

Sleep deprivation and/or exhaustion. Physical and emotional exhaustion can induce hallucinations by blurring the line between sleep and wakefulness.
Medications: A number of drugs taken for long periods of time or in excessive dosages can cause symptoms of Parkinson's disease. These include medications such as haloperidol (Haldol) and chlorpromazine (Thorazine), which are prescribed for certain psychiatric disorders, as well as drugs used to treat nausea, such as metoclopramide (Reglan, Metoclopramide HCL). The epilepsy drug valproate (Depakene) also may cause some of the features of parkinsonism, especially severe tremor.

Electrical or neurochemical activity in the brain: A hallucinatory sensation--usually involving touch--called an aura, often appears before, and gives warning of, a migraine. Also, auras involving smell and touch (tactile) are known to warn of the onset of an epileptic attack.
Brain damage or disease: Lesions or injuries to the brain may alter brain function and produce hallucinations.