Delirium or Dementia: The Distinction Every Carer Should Learn

Confusion that arrived over a day or two and comes and goes through the day is delirium until proven otherwise. Confusion that has crept up over months and is broadly the same from hour to hour is more likely dementia. The first is a phone call today; the second is an appointment to book. That single distinction is the most useful thing a family carer can learn, because you are the only person in the whole system who knows what the person was like last Tuesday.

Delirium is a clinical syndrome characterised by disturbed consciousness, cognitive function or perception, which has an acute onset and fluctuating course, and it usually develops over 1 to 2 days (NICE guideline CG103, published July 2010, substantively updated 18 January 2023)¹. It is common, it is frequently missed, and, in NICE’s own words, “it can be prevented and treated if dealt with urgently”¹.

My mother spent two days after her coronary bypass surgery not making sense. She thought she was in the wrong building, she could not follow the end of a sentence, and by the third morning she was completely herself again. I was told it was probably the anaesthetic and I accepted that, because I had no word for what I had watched. I learned the word about a year later. Between 10 and 50 percent of people having surgery develop delirium¹, and nobody used the term in front of me once.

This article sits under caring for a parent at home and pairs with spotting when someone is getting worse.

What is the difference, in one table?

Speed, fluctuation and attention are the three things to look at. Memory is the least useful of the four, because both conditions affect it.

	Delirium	Dementia
Onset	Acute, usually over 1 to 2 days	Gradual, over months and years
Course through the day	Fluctuates, often worse in the late afternoon and at night	Broadly stable from hour to hour
Attention	Disturbed: cannot hold the thread of a sentence or follow a simple instruction	Relatively preserved until late in the illness
Alertness	Altered: either agitated and restless, or withdrawn, drowsy and slow	Normal
Duration	Days to weeks, sometimes longer	Years, and progressive
Reversibility	Often reversible if the cause is treated urgently	Not reversible, though treatable and manageable
What it means for you	Ring today	Book an appointment, and start planning

NICE’s own description of the difficulty is worth having in front of you: “It can be difficult to distinguish between delirium and dementia and some people may have both conditions.”¹ A caveat on attribution, because it is widely got wrong: the familiar four-feature formulation of delirium, meaning acute onset plus fluctuating course plus inattention plus altered consciousness or disorganised thinking, comes from the Confusion Assessment Method developed by Inouye and colleagues, not from NICE.

For the wider dementia picture, see dementia care at home. Worldwide, 57 million people were living with dementia in 2021, with nearly 10 million new cases every year and Alzheimer’s disease contributing to 60 to 70 percent of cases (WHO fact sheet, page dated 3 July 2026)².

How common is delirium?

Common enough that a carer should expect to meet it. NICE reports that “the prevalence of delirium in people on medical wards in hospital is about 20% to 30%, and 10% to 50% of people having surgery develop delirium. In long-term care the prevalence is under 20%“¹. For intensive care, SIGN 157 records up to 50 percent among people who have had a hip fracture and up to 75 percent in intensive care (published March 2019, revalidated 2022, Scotland)³.

It is also badly under-recorded. NICE notes that “reporting of delirium is poor in the UK, indicating that awareness and reporting procedures need to be improved”¹. That is the reason this page exists: the gap is not usually clinical difficulty, it is that nobody raised it.

Why is the quiet kind the one that gets missed?

Because it looks like being tired, or being low, or being old, and none of those things sets off an alarm. The agitated form of delirium is hard to ignore. The hypoactive form is very easy to ignore, and it is the more common of the two in older people.

NICE addresses it directly, and the wording is worth memorising: “Be particularly vigilant for changes that may indicate hypoactive delirium, which are often missed, such as withdrawal, slow responses, reduced mobility and movement, worsened concentration and reduced appetite.”¹

If somebody who normally talks has gone quiet, if they are sleeping in the day when they never did, if they have stopped finishing meals, or if they seem to be looking through you rather than at you, that is not necessarily a bad week. Treat it with the same urgency as agitation.

What will happen when you ring?

An assessment, and it is quick. NICE recommendation 1.6.1, updated in 2023, says that if indicators of delirium are identified, a health or social care practitioner who is competent to do so should carry out an assessment using the 4AT, and that in critical care or in the recovery room after surgery the CAM-ICU or the Intensive Care Delirium Screening Checklist is used instead¹. The 4AT was developed by Professor Alasdair MacLullich and colleagues at the University of Edinburgh, is brief, and needs no special training to administer⁴.

NICE also expects daily observation of people at risk, documentation of any changes, and a final diagnosis made by a professional with relevant expertise¹. What that means in practice is that raising it is not a nuisance. It is the trigger for a defined process.

Then comes the search for a cause, because delirium is a symptom rather than a diagnosis in itself. Expect questions about infection, fluids, bowels, pain, urinary retention and, very often, medicines. If the list has grown long over the years, ask for a structured medication review: NICE guideline NG5 recommends considering one for people taking multiple medicines, people with long-term conditions and older people, taking into account the carer’s views as well as the person’s⁵. No page on this site will tell you to give, stop or change anything. That is the prescriber and the pharmacist, and managing someone else’s medication covers how to ask.

Which comes first if you cannot tell?

Delirium, always, and this is written into the guidance. NICE recommendation 1.6.3, verbatim: “If there is difficulty distinguishing between the diagnoses of delirium, dementia or delirium superimposed on dementia, manage the delirium first.”¹

The logic is straightforward. Delirium is the part that can be treated urgently, and treating it is what reveals what the underlying baseline actually is. A great many families have been told their relative had “gone downhill with the dementia” during an admission, when what they had was an untreated infection on top of it. Delirium superimposed on dementia is common, and people with dementia are at higher risk of it.

This is why your record matters more than you think. Keeping a care file sets out how to log a change with a date, and being heard in appointments covers getting that information into a ten minute slot. A dated note saying “on the 4th she was doing the crossword and on the 6th she could not follow a sentence” does more work than any adjective.

What to say on the phone

Lead with the comparison and the timing, then the specifics. A structure that works:

1. “She was herself last week. Since Tuesday she has been confused, and it comes and goes.” Timing and fluctuation first.
2. “I think this might be delirium.” Say the word. It changes the speed of the response, and carers rarely know they are allowed to use it.
3. Attention: can they hold the thread of a sentence, follow a simple instruction, or are they losing track mid-answer.
4. Alertness: more agitated or more drowsy than normal.
5. The obvious causes: eating and drinking, urine, bowels, fever, pain, any fall, any new or changed medicine, and anything that happened recently such as a hospital stay or a general anaesthetic.
6. What you need: an assessment today, and the name of who will do it.

Do not open with “I do not want to waste your time”. You are the second chair in the room, and you are holding the only baseline anybody has. Detection is exactly where this condition fails: NICE records that “reporting of delirium is poor in the UK, indicating that awareness and reporting procedures need to be improved”¹.

After a hospital stay, and after a fall

Two situations deserve extra vigilance because they concentrate the risk.

After a discharge. The rate of delirium among people having surgery runs from 10 to 50 percent¹, and the days after coming home are exactly when nobody is watching. NICE guideline NG27 says a GP or community-based nurse should phone or visit people at risk of readmission 24 to 72 hours after their discharge⁶. If that has not happened and something has changed, make the call yourself. Coming home from hospital covers the whole discharge window.

After a fall. A fall can be the first sign of delirium as easily as the result of one, and around a third of people aged 65 and over fall at least once a year, with a one-year mortality rate of 31 percent after a hip fracture (NICE guideline NG249, published April 2025)⁷. SIGN records delirium in up to 50 percent of people who have had a hip fracture³. Confusion plus a fall is not two problems; it is usually one. Falls at home covers the first minutes and the assessment to ask for.

What recovery looks like, and what it does not

Recovery from delirium is frequently slower than families are led to expect. Days is common, weeks is normal, and some people do not return fully to the baseline they had before. NICE calls delirium “a serious condition that is associated with poor outcomes” in the same breath as saying it can be prevented and treated if dealt with urgently¹, and both halves of that are true at once: urgency helps, and it does not guarantee a clean return. That is a genuinely hard thing to be told, and it is another argument for having written down what the baseline was.

If the confusion resolves and something is still different, ask for a follow-up assessment rather than assuming the answer. NICE advises clinicians that carers of people living with dementia are at increased risk of depression⁸, which is worth knowing about yourself as well as about them: carer burnout and your own health sets out what the evidence really shows, including where the popular claims overstate it.

This is a call today, not something to watch overnight

Ring the same day, and use the word confusion, if the person you look after:

• Is more confused than they were yesterday, or the confusion comes and goes through the day.
• Has become withdrawn, slow, drowsy, or has stopped finishing meals, which is the quiet form and the one most often missed¹.
• Cannot hold attention on a sentence or a simple instruction when they could last week.
• Is seeing or hearing things that are not there, or is frightened of things that do not usually frighten them.
• Has a fever, has stopped drinking, has not passed urine, or is in new pain.
• Has had a fall, or has recently come out of hospital or had an anaesthetic.

Who to ring: in the United Kingdom, their GP surgery, or NHS 111 out of hours. In the United States, their doctor’s office, or the nurse line their plan runs, or urgent care. In Australia, their GP, or healthdirect on 1800 022 222. In Canada, their family doctor or the provincial health line, 811 in most provinces. In Ireland, their GP or the out of hours GP service.

Use the emergency number immediately for changed breathing, chest pain, one-sided weakness, changed speech, a first seizure, an unrousable person, or bleeding that will not stop: 999 or 112 in the United Kingdom and Ireland, 911 in the United States and Canada, 000 in Australia.

Delirium is not a wait and see condition, and nothing on this page is a reason to give it until the morning. The causes that arrive that fast are usually the ones that can be fixed, and they get harder to fix the longer they run.