Hallucinations: Seeing or Hearing Things That Are Not There

Types of hallucinations

Hallucinations differ from illusions, which are misinterpretations of real things (a coat on a door looks like a person), and from delusions, which are fixed false beliefs.

Causes of hallucinations

Medical and neurological causes

• Delirium: a sudden change in attention and thinking caused by infection (such as a urinary tract infection or pneumonia), dehydration, surgery, low oxygen, low sodium or medicines. Visual hallucinations, agitation and fluctuating confusion are common, especially in older adults. It is a medical emergency, but usually reversible.
• Dementia with Lewy bodies: detailed visual hallucinations of people or animals early in the illness, with fluctuating alertness and Parkinson-like stiffness.
• Parkinson's disease: visual hallucinations develop in many people over time, often triggered by medicines. They may start as a sense of a presence or something passing at the side of vision.
• Alzheimer's disease: hallucinations occur in later stages.
• Epilepsy: focal seizures in the temporal lobe can cause brief smells, tastes, déjà vu or sounds.
• Migraine: visual aura of zigzag lines or flashing lights lasting 5 to 60 minutes.
• Brain tumors, stroke and encephalitis.
• High fever, especially in children and older adults.

Eye and ear conditions

• Charles Bonnet syndrome: vivid, silent visual hallucinations in people with significant vision loss, such as from macular degeneration. The person knows they are not real. It is not a mental illness.
• Musical ear syndrome: hearing music or singing in people with hearing loss.

Medicines, alcohol and drugs

• Parkinson's medicines (levodopa, dopamine agonists), steroids, opioids, some antibiotics, anticholinergics and sleeping medicines, especially in older adults.
• Alcohol withdrawal: hallucinations can start 12 to 48 hours after the last drink. Delirium tremens, usually 48 to 96 hours after, is life-threatening.
• Recreational drugs: LSD, psilocybin, ketamine, cannabis (especially high-potency), cocaine and methamphetamine. See substance-induced psychosis.

Mental health conditions

• Schizophrenia: hearing voices that comment on or talk to the person is the most typical hallucination, often with delusions and disorganized thinking.
• Bipolar disorder and severe depression with psychotic features.
• Postpartum psychosis: a rare emergency in the first weeks after childbirth.
• PTSD: flashbacks can include sensory re-experiencing.
• Severe stress and sleep deprivation.

Hallucinations that are not usually a sign of illness

• Hypnagogic hallucinations when falling asleep or waking are common in healthy people, especially when sleep-deprived. Frequent ones with daytime sleepiness and sleep paralysis can suggest narcolepsy.
• Bereavement: hearing or sensing a loved one after their death is common and often comforting.
• Sensory deprivation, such as long periods in darkness or isolation.

Hallucinations in older adults

In older people, new hallucinations are most often caused by delirium, medicines, dementia, Parkinson's disease or vision loss rather than a primary psychiatric illness. A sudden change over hours or days, with confusion or drowsiness, suggests delirium and needs same-day medical assessment for infection, dehydration, medicine side effects and other triggers.

How doctors find the cause

A doctor will ask what the person experiences, when it started, whether it comes and goes, whether they know it is not real, sleep, alcohol and drug use, all medicines, and other symptoms. They will check vital signs, mental state, eyes, hearing and neurological function.

Tests may include:

• blood tests: blood count, electrolytes, sodium, calcium, glucose, kidney, liver and thyroid function
• urine test for infection and drug screen
• oxygen level
• brain imaging (CT or MRI) for new neurological symptoms
• EEG if seizures are suspected
• eye and hearing tests
• mental health assessment

Treatment

Treatment targets the cause:

• Delirium: treat the infection, dehydration or medicine problem. Calm, well-lit surroundings, glasses and hearing aids, and familiar people help.
• Withdrawal: medically supervised detox with benzodiazepines and thiamine.
• Medicines: a doctor may lower or change the dose. Do not stop prescribed medicines suddenly yourself.
• Psychotic disorders: antipsychotic medicines, talking therapies such as cognitive behavioral therapy for psychosis, and support services. Early treatment improves outcomes.
• Parkinson's and Lewy body dementia: medicine review. Pimavanserin or low-dose quetiapine or clozapine may be used. Many standard antipsychotics can cause severe reactions in Lewy body dementia and should be avoided.
• Charles Bonnet syndrome: reassurance, better lighting, and eye movements or blinking can stop an episode.

How to support someone who is hallucinating

• Stay calm and speak simply.
• Do not argue about whether the hallucination is real, but do not pretend to share it. Acknowledge their feelings.
• Reduce noise and shadows, and turn on lights.
• Keep them safe, and call 911 if they or others are at risk.

Frequently asked questions

What causes hallucinations?

Hallucinations can be caused by mental health conditions such as schizophrenia and bipolar disorder, but also by delirium, dementia, Parkinson's disease, epilepsy, migraine, vision or hearing loss, medicines, alcohol withdrawal, recreational drugs, high fever and severe sleep deprivation.

Are hallucinations always a sign of mental illness?

No. Many hallucinations have physical causes, such as infection, medicines, withdrawal, dementia or eye disease. Brief hallucinations when falling asleep or waking are common in healthy people. Any new or persistent hallucinations should still be checked by a doctor.

Why is an elderly person suddenly seeing things?

Sudden hallucinations in an older adult are often caused by delirium, triggered by an infection such as a urinary tract infection, dehydration, a new medicine or surgery. Dementia, Parkinson's disease and vision loss are other causes. A sudden change needs same-day medical assessment.

What is the difference between auditory and visual hallucinations?

Auditory hallucinations involve hearing sounds or voices and are more typical of psychiatric conditions such as schizophrenia. Visual hallucinations involve seeing things and more often point to medical or neurological causes such as delirium, Lewy body dementia, drugs or eye disease.

Can lack of sleep cause hallucinations?

Yes. Severe sleep deprivation, typically after 24 to 48 hours or more without sleep, can cause visual hallucinations, perceptual distortions and paranoia. Hypnagogic hallucinations when falling asleep are also more frequent when you are sleep-deprived. They stop with adequate sleep.