Delirium and Sudden Confusion

Delirium is a sudden change in a person's awareness, thinking or behaviour. It can develop over hours or days.

It usually lasts a short time, but it is always serious and needs a medical assessment to find the cause [1][4].

It is more common in older people and people with dementia, but it can happen at any age, especially during serious illness or after surgery [4].

A person may:

• not be able to think or speak clearly or quickly
• not know where they are, or what time or day it is
• struggle to pay attention or remember things
• see or hear things that are not there
• become agitated, restless, frightened or suspicious
• become unusually quiet, withdrawn, slow or sleepy
• be unsteady or more likely to fall

Quiet and sleepy delirium is easy to miss. Symptoms can also come and go during the day, and are often worse at night. A person may seem well, then confused again [4].

The NHS suggests asking the person their name, age and today's date. If they seem unsure or cannot answer, they probably need medical help [1].

Family and friends are often the first to notice small changes. Trust what you see.

Do not try to work out the cause yourself. Common causes listed by the NHS include [1]:

• an infection, including a UTI
• a stroke or TIA ("mini-stroke")
• low blood sugar in people with diabetes
• a head injury
• some prescription medicines
• alcohol poisoning or alcohol withdrawal, or taking drugs
• carbon monoxide poisoning, especially if others at home also feel unwell
• a severe asthma attack or other heart or lung problems
• certain types of seizure

Hospital teams also check for dehydration, constipation, being unable to pass urine and abnormal blood results [4].

A UTI can cause confusion or changes in behaviour, especially in older people and people with dementia [1][2]. But it is only one possible cause.

Never assume sudden confusion is "just a UTI". The person needs to be assessed. Do not give antibiotics unless a doctor, nurse or pharmacist has prescribed them for this illness.

NHS information about UTIs →

A person with dementia can also develop delirium. A sudden change is never "just the dementia" until a professional has checked [1][4].

Doctors and nurses look for causes that can be treated, such as infection, dehydration or medicine side effects. Some people need hospital care; others can be treated at home [4].

Sometimes calming medicine is used, but only if the person is still distressed or unsafe after other ways of keeping them calm have been tried [4].

Delirium often improves, but everyone is different. Some people take longer, and some do not fully return to how they were, particularly people with dementia [4]. Ask the care team what to expect for your relative.

• Tell staff what the person is normally like. You know them best.
• Bring familiar things: glasses, hearing aids, photos or a clock.
• Help with drinks, meals and moving about, if staff agree.
• Talk calmly about familiar people and places.
• Before they leave hospital, ask about extra support and preventing falls at home [4].

Delirium can be frightening for everyone. Not everyone remembers it; those who do may find the memories upsetting. Talking about it afterwards can help [4].

Look after yourself too. Carers' support services are listed in our support directory.

Information checked 27 October 2026. Each source's own review dates are shown in the references below.

This page is general information, not a diagnosis or a replacement for professional medical care. In an emergency, call 999.