Mind
Sudden confusion or delirium
A rapid change in thinking, awareness or behaviour that develops over hours or days, which is a medical emergency because it can be the first sign of a serious infection, a stroke, or another urgent illness.
Education and reference only. This explains the common causes of sudden confusion or delirium and the warning signs that need urgent help, in plain language — it is not a diagnosis or a substitute for advice from a clinician. If you feel very unwell or are worried, seek medical help.
Quick answer
What is sudden confusion or delirium?
Sudden confusion, sometimes called delirium, means becoming muddled, disorientated, drowsy or agitated over a short period — hours to a few days — rather than the slow, gradual decline seen in dementia. The person may not know where they are or what time it is, may be unusually restless or sleepy, and may see or believe things that are not real.
- Get urgent help: New, sudden confusion can mean sepsis, a stroke or a serious infection — seek urgent help, and call 999 if the person is very unwell. Confusion with FAST signs — face drooping, arm weakness or slurred speech — call 999, as this can be a stroke.
- Self-care: Sudden confusion is not something to manage at home with self-care; the priority is to get urgent medical help, because the cause is often serious and treatable.
About sudden confusion or delirium
Sudden confusion, sometimes called delirium, means becoming muddled, disorientated, drowsy or agitated over a short period — hours to a few days — rather than the slow, gradual decline seen in dementia. The person may not know where they are or what time it is, may be unusually restless or sleepy, and may see or believe things that are not real. This is always a warning sign that something is wrong in the body, and the underlying cause is often serious and treatable. Common triggers include infection of any kind, such as a urinary-tract-infection or kidney-infection, dehydration, low blood sugar, a stroke, or the effects of new medicines, and in serious infection it can be a sign of sepsis. Older people and those with existing dementia are especially prone to becoming acutely confused when unwell. Because the cause can be life-threatening, new sudden confusion should be treated as an emergency.
When to get help
Call 999 or go to A&E if sudden confusion or delirium comes with any of these warning signs:
- New, sudden confusion can mean sepsis, a stroke or a serious infection — seek urgent help, and call 999 if the person is very unwell.
- Confusion with FAST signs — face drooping, arm weakness or slurred speech — call 999, as this can be a stroke.
- Confusion with a fever, a very low temperature, shivering, fast breathing, a rash or feeling extremely unwell — call 999, as this can be sepsis.
- Confusion after a head injury, a fall, or with a severe headache — seek emergency help.
- Confusion with drowsiness that is hard to rouse, or a fit (seizure) — call 999.
When to see a doctor
Treat any new, sudden confusion as a medical emergency and seek urgent help, calling 999 if the person is very unwell, drowsy, or showing signs of a stroke or sepsis. This is different from the slow, gradual memory decline of dementia, which can be assessed at a routine appointment. Be especially alert in older people and those with existing dementia, in whom an infection may show itself mainly as a sudden change in alertness, behaviour or thinking rather than the usual symptoms. The sooner the underlying cause is found and treated, the better the outcome, so do not wait to see whether confusion settles on its own.
Not sure how urgent it is? It is always OK to call NHS 111 for advice, day or night.
What can cause it
Common causes of sudden confusion or delirium
Sudden confusion or delirium has many possible causes. Each links to a full, plain-language guide to that condition — what it is, how it's treated and when to seek help.
What helps
Self-care and what you can do
Sudden confusion is not something to manage at home with self-care; the priority is to get urgent medical help, because the cause is often serious and treatable. While arranging help, keep the person safe and calm: stay with them, speak gently and clearly, reduce noise and bright or dim lighting that may disorientate them, and make sure they are not at risk of falling or wandering. Offer sips of fluid if they are alert and able to swallow safely. Note when the confusion started, how quickly it came on, and anything that might be relevant such as fever, a fall, a new medicine, or recent illness, as this helps the clinician find the cause quickly. Do not leave a suddenly confused person alone if you can avoid it.
Answers
Sudden confusion or delirium: frequently asked questions
How is sudden confusion different from dementia?
Sudden confusion (delirium) develops over hours or days and is usually caused by a physical illness such as infection. Dementia develops slowly over months and years. New, rapid confusion is an emergency and needs urgent assessment to find the cause.
Can a urine infection really cause confusion?
Yes, especially in older people, in whom a urinary-tract infection may cause sudden confusion without the usual burning or frequency. This is why new confusion always needs a physical check rather than being assumed to be due to age.
Why is sudden confusion an emergency?
Because the cause is often serious and treatable, including sepsis, stroke and severe infection. Treating it quickly can be life-saving, so new sudden confusion should never be left to settle on its own.
What should I do while waiting for help?
Stay with the person, keep them calm and safe from falls, reduce noise and disorientating light, and offer sips of fluid if they can swallow safely. Note when the confusion started and any fever, fall or new medicine to tell the clinician.
Sources
Where this is drawn from
- NICE CKS: Delirium.
- UK Sepsis Trust
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