Hallucinations are when you hear, see, smell, taste or feel things that seem real but only exist in your mind. They have many causes, and not all of them are a mental health condition.
The NHS says some hallucinations are temporary. They can happen as you fall asleep or wake up, or with a high temperature. Migraines, hunger and lack of sleep can also cause them. Others come from sight loss, medicines, alcohol or drugs, dementia, Parkinson's disease, or a mental health condition such as psychosis.
You cannot tell which from the experience alone. The NHS advises an urgent GP appointment for anyone having hallucinations. Some situations need emergency help, set out below.
Get help now
Call 112 or 999 in Ireland, 999 in the UK or 911 in the US, or go to an emergency department, if you or someone else:
Do not drive yourself. Ask someone to drive you, or call for an ambulance.
Get an urgent GP appointment the same day if:
In the UK you can also call NHS 111. In Ireland, contact your GP or out-of-hours GP.
If you are having thoughts of suicide or self-harm: in Ireland, freephone Samaritans on 116 123 or text 50808. In the UK, call Samaritans on 116 123. In the US, call or text 988.
The NHS describes several types. You may:
The HSE says hallucinations feel very real to the person having them, even though people around them cannot experience them.
The NHS lists hallucinations "just as you wake up or fall asleep" among temporary causes. Some people sense a presence in the room or hear sounds as they drift off.
This can come with sleep paralysis. In sleep paralysis, the NHS says you may feel awake but unable to move. You may feel someone is in your room, or something pushing you down. It says it can be scary, but it is harmless. It has been linked with insomnia, disrupted sleep such as shift work, narcolepsy, PTSD and anxiety disorders.
If this happens often, with daytime sleepiness or sudden muscle weakness, read about why narcolepsy diagnosis takes years.
The NHS says hallucinations can happen with a high temperature, migraines, when you are very hungry or when you are sleep deprived. They can also happen after surgery and anaesthesia.
The NHS says Charles Bonnet syndrome can cause visual hallucinations if you have lost a lot of your sight. It is often linked to age-related macular degeneration or cataracts. It is not caused by a mental health problem or dementia.
The hallucinations can be patterns, people, animals, objects or places. They can last minutes or hours. They are only things you see, not hear or smell. Most people know they are not real.
The NHS still advises an urgent GP appointment, to rule out more serious causes. It says the hallucinations usually happen less often over time. If they suddenly return or get worse, an infection or a medicine could be the cause.
Things the NHS suggests trying during a hallucination include changing the lighting, moving your eyes from side to side, and standing up and moving around.
The NHS describes psychosis as losing some contact with reality. The main symptoms are:
The HSE says a person in a psychotic episode may not be aware that their experiences are not real. They may feel frightened or distressed.
The NHS says causes include schizophrenia, bipolar disorder and severe depression. Psychosis can also be triggered by trauma, stress, drug misuse, alcohol-use disorder, medicines, physical illness, head injury and childbirth. The NHS lists severe stress or anxiety and lack of sleep among psychological causes too.
It is important to get help early. The NHS says to see a GP immediately, as early treatment can be more effective.
The HSE notes that psychosis is not the same as being a "psychopath". It says people with psychosis are more likely to harm themselves than others.
The HSE lists hearing or smelling things that are not there among possible symptoms of both the depressive and manic phases of bipolar disorder. The NHS says some people with depression have symptoms of psychosis when they are very depressed. Read our guide to bipolar disorder in adults.
The NHS describes postpartum psychosis as a serious mental illness that should be treated as a medical emergency. It affects around 1 in 1,000 mothers. Symptoms usually start suddenly within the first 2 weeks after birth. They include hallucinations, delusions, mania, low mood and confusion.
The NHS says the person may not realise they are ill, so partners, family or friends may have to act. Most people make a full recovery with the right treatment. Our postpartum depression guide explains how it differs from the baby blues and postnatal depression.
The NHS lists severe depression and post-traumatic stress disorder among the common causes of hallucinations.
The NHS says alcohol-use disorder and drug misuse can trigger psychosis. So can withdrawal, when someone suddenly stops after using them for a long time. Drugs it names include cannabis, cocaine, amphetamines, MDMA, LSD, magic mushrooms and ketamine.
Some prescribed medicines can cause hallucinations as a side effect, though the NHS says psychosis from medicine is rare. One example is Parkinson's disease: the NHS says dopamine agonists can cause hallucinations and more confusion, especially in older people.
Never stop a prescribed medicine on your own. The NHS says to see a GP if you think a medicine is causing psychotic side effects.
Sudden confusion (delirium). The NHS says hallucinations can come with infection or delirium, especially in older people. Sudden confusion needs emergency help.
Dementia with Lewy bodies. The NHS lists hallucinations among the symptoms that help tell it apart from other dementias. They can range from pleasant to distressing. Other signs include swings between alertness and confusion, and slow, stiff movement. Read why Lewy body dementia gets missed.
Parkinson's disease. The NHS lists visual hallucinations and delusions as part of the dementia that can develop in Parkinson's. See our guide to Parkinson's disease treatment.
Other medical conditions. The NHS says psychosis can be triggered by low blood sugar, lupus, multiple sclerosis, brain tumours, high fever or head injury.
The HSE says there is no single test to diagnose psychosis. A GP will ask about your symptoms and possible causes, including:
It helps to note when the experiences happen. Say whether they come at the edge of sleep, with fever or illness, or after a change in medicine. Mention any sight loss.
A GP may refer you to a community mental health team, which may include a psychiatrist. For visual hallucinations with sight loss, an eye check may be needed. For an older person, tests depend on whether delirium or dementia is suspected.
The NHS says treatment for hallucinations depends on what is causing them. A GP may suggest drinking less alcohol, not taking drugs and getting more sleep.
For psychosis, the NHS says treatment usually combines antipsychotic medicine, talking therapies such as cognitive behavioural therapy (CBT) and family interventions, and social support.
The HSE says someone may not want to see a GP if they believe nothing is wrong. You may need to help them get support. If they have a key worker or mental health team, contact them.
The NHS says you can contact a GP for them. If their symptoms are severe and could put them at risk, take them to an emergency department if they agree, or call for an ambulance.
The NHS says people with psychosis have a higher than average risk of self-harm and suicide. Please reach out.
The NHS lists hallucinations as you fall asleep or wake up as a temporary cause. Sleep paralysis can feel frightening but is harmless. Mention it to a GP if it happens often or comes with daytime sleepiness.
Not necessarily. Hearing voices is a common hallucination in psychosis, but the NHS lists many other causes. These include lack of sleep, drugs, alcohol, medicines and severe depression. A GP can help work out the cause.
The NHS lists sleep deprivation as a temporary cause. It also lists severe stress, anxiety and lack of sleep as possible triggers for psychosis. See a GP if hallucinations happen.
Get an urgent GP appointment. If they are also suddenly confused, call 112, 999 or 911. Possible causes include delirium, sight loss (Charles Bonnet syndrome), medicines, and dementia with Lewy bodies.
This article is general information, not medical advice. It cannot diagnose the cause of anyone's symptoms. Talk to your GP about your own symptoms, and before starting, stopping or changing any medicine.
Reviewed by: Proco Team
Last updated: November 2026