Seeing things that aren’t there

Simple visual experiences, like flashing lights or zigzag lines, are typical of migraine aura. Patterns and shapes are also common in Charles Bonnet syndrome.

Some people see detailed images, such as people, animals, objects or places. In Lewy body dementia, they are often realistic, such as children or animals.

Not every unusual sight is a full hallucination. With severe sleep loss, people often first notice distortions and illusions, where real objects look different, before seeing things that aren’t there.

Most people with Charles Bonnet syndrome know the images aren’t real. In Parkinson’s, some people keep this insight, while others find the images very real, especially as the condition progresses.

In a UK survey, 37% of people had hallucinations when falling asleep and 12.5% when waking up. They were more common with insomnia and daytime sleepiness.

A review of studies with healthy volunteers found changes in vision in 90% of studies. Changes began within 24 to 48 hours awake and grew with time. Normal sleep resolved the symptoms in many, but not all, cases.

Images can be moving or still, in colour or black and white, and can start suddenly. Episodes can last a few minutes or several hours. The hallucinations are only visual.

It is more likely if sight gets worse suddenly or both eyes are affected. About 1 in 5 people aged 40 and over with low vision have it.

Tips from the NHS

• Change the lighting: brighter if it’s dark, dimmer if it’s bright
• Get enough rest, as tiredness and stress can make it worse
• Look side to side without turning your head, 15 to 30 times, then pause and repeat
• Reach out to touch the image, or check with a cane
• Stand up and move, or watch TV or listen to the radio

There is no cure, but the images usually become less frequent over time. A low-vision service can help too.

These can be signs of a detached retina, which is a medical emergency. Contact an eye doctor or go to an emergency room straight away. Quick treatment can help protect your sight.

Aura usually comes before the headache. As well as zigzags or flashing lights, some people get pins and needles, dizziness or difficulty speaking.

Aura should not last longer than an hour. If it does, get urgent medical advice.

Call 911 if someone has

• A sudden, extremely painful headache
• Loss of vision, or blurred or double vision
• Problems speaking or remembering
• Weakness on one side of the body or face

The NHS lists a high temperature and being very hungry as temporary triggers. An infection can also cause sudden confusion, called delirium, especially in older people.

Someone with delirium may not think clearly, not know where they are, struggle to pay attention, and see or hear things that aren’t there. Ask their name, age and today’s date. If they can’t answer, get medical help.

Most people with Lewy body dementia have visual hallucinations, often early in the disease. They are usually realistic and detailed. If they aren’t upsetting, they may not need treatment.

20–40% of people with Parkinson’s report hallucinations or delusions, and seeing things is the most common. Low light makes visual hallucinations more likely.

In some focal seizures, a person stays aware but may see, hear, smell, taste or feel things that are not real. Seizures starting in some parts of the brain can cause visual hallucinations.

The NHS lists surgery and anaesthesia as possible causes. Tell the care team about anything new you notice while recovering.

People who use psychedelics often report seeing vivid shapes, colours and scenes. Flashbacks are usually mild and brief, but a rare condition can bring back visual changes even years later.

NIDA lists hallucinations, fear and panic among short-term effects of cannabis, especially at high doses. It can also bring on a temporary psychotic episode in some people.

Delirium tremens is a severe form of alcohol withdrawal. It can bring hallucinations, sudden severe confusion, fever and seizures. Symptoms often peak 24 to 72 hours after the last drink.

A review found that 47% to 82% of bereaved people in different studies sensed their loved one in some way. Feeling their presence is most common. Hearing them is common too, and seeing them is less often reported.

Most of these experiences are felt as comforting, and the review concludes they don’t generally point to a mental health problem.

The NHS lists post-traumatic stress disorder among conditions that can cause hallucinations.

Hallucinations in schizophrenia, bipolar disorder and severe depression can involve any sense. Hearing voices is the most common kind.

You might say

• “Don’t worry. I’m here.”
• “I know this is frightening for you.”
• “I can see you’re seeing something, but I don’t see it.”

A calm, practical response can help too. The Parkinson’s Foundation gives the example of saying “I’ll take the cat outside” rather than insisting there is no cat.

Things to try

• Add light to cut down shadows, especially in hallways
• Cover or remove mirrors if they see a “stranger” in them
• Move to another room, or go for a short walk together
• Turn down the TV or other background noise

The Alzheimer’s Association suggests first asking whether the hallucination is upsetting the person or putting them in danger. If it is pleasant and harmless, you may not need to do anything.

Report all hallucinations to the person’s care team, even small ones. A medical check can find causes such as infection, eyesight or hearing problems.