How can I tell delirium apart from dementia?

The biggest clue is speed. Delirium appears suddenly (hours to days) and comes and goes through the day; dementia creeps in slowly over months to years and is fairly steady. If someone with known dementia gets abruptly and noticeably worse, treat it as possible delirium and seek help.

My relative has become very quiet and sleepy in hospital – is that delirium?

It can be. Quiet, drowsy withdrawal is hypoactive delirium, the type most often missed. Don’t assume it’s just tiredness – mention the change to the nurses or doctor and ask whether delirium has been considered.

Is delirium a sign my relative is getting dementia?

Not necessarily. Delirium is usually caused by a treatable physical problem and often resolves. However, an episode can unmask underlying brain vulnerability, so a follow-up review of memory and thinking after recovery is sensible.

What can I do as a family member to help?

Give staff a clear picture of the person’s normal self, bring in glasses, hearing aids and familiar items, visit to provide reassurance and gentle reorientation, encourage fluids and eating, help them stay mobile, and support good sleep. Your presence and history are part of the treatment.

Delirium (Sudden Confusion) Singapore

Written & reviewed by the BestDoctors.sg editorial team · Last updated 24 Aug 2026 · General information, not medical advice

Quick answer. Delirium is a sudden change in a person’s mental state – new confusion, reduced awareness and muddled thinking – that develops over hours to days and typically fluctuates through the day, often worse at night. In an older person it is a medical emergency and usually a sign of a treatable physical problem (such as an infection), so any sudden confusion warrants prompt assessment at A&E – not “wait and see,” and not simply “the dementia getting worse.”

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In a medical emergency, or for severe or sudden symptoms such as breathing difficulty, chest pain, fainting or stroke signs, call 995 immediately.

The single most useful clue: speed. Delirium comes on over hours to days and comes and goes; dementia develops slowly over months to years and is fairly steady.

What delirium is – and how it differs from dementia

Delirium (an “acute confusional state”) is a sudden disturbance of attention, awareness and thinking. The person may be unable to follow a conversation, lose track of where they are, or drift in and out of alertness. The hallmark is change and fluctuation – someone can seem almost normal in the morning and very confused by evening. This differs from dementia, which comes on slowly over months and years. The two are linked: dementia is the biggest risk factor for delirium, and delirium can be layered on top of dementia (a sudden worsening in someone with dementia should be treated as possible delirium).

The two types – and why the quiet one is missed

Hyperactive delirium: restlessness, agitation, trying to get out of bed, pulling at drips, irritability, sometimes hallucinations – distressing but obvious;
Hypoactive delirium: withdrawn, sleepy, slow to respond, quiet and uninterested – easily dismissed as “tired” or “a bit down.” This type is the most frequently missed and tends to have worse outcomes;
Mixed: features of both, switching between them.

So any new drowsiness or withdrawal in an older person deserves the same concern as agitation.

What triggers it

Delirium is the brain’s response to physical stress. Common triggers include: infection (urine and chest infections are classic – confusion may be the first sign, before fever); dehydration, constipation or a full bladder; poorly controlled pain; medicines (newly started drugs, side effects, or withdrawal, including alcohol); low oxygen; recent surgery and anaesthesia; electrolyte or blood-sugar upsets; and the unfamiliar hospital environment. In frail or older people, several of these often occur at once.

Who is most at risk

Risk rises with older age, existing dementia or previous delirium, frailty, poor eyesight or hearing, severe illness, multiple medicines, and being in hospital or after an operation.

How it’s diagnosed and managed

There’s no single blood test – delirium is recognised clinically by spotting the sudden change and fluctuation, which is why collateral history from family (“she was completely fine two days ago”) is so important. Doctors then search for and treat the cause. Management has two arms: (1) find and treat the underlying cause (antibiotics for infection, fluids for dehydration, relieving constipation, controlling pain, reviewing culprit medicines); and (2) supportive care – reassure and gently reorient, keep glasses and hearing aids on, protect sleep, keep the person hydrated and mobile, and avoid unnecessary catheters, restraints and sedatives (which tend to worsen delirium). Recovery can take days to weeks and isn’t always complete – and delirium can often be prevented through these same good-care measures.

Delirium in someone with dementia

Delirium and dementia often occur together, and telling them apart is one of the most useful things a family can do. Someone with dementia who suddenly becomes much more confused, agitated or drowsy than their usual self – over hours or a day or two – is very likely developing delirium on top of their dementia, not simply “getting worse.” This matters because the delirium usually has a treatable cause, such as an infection, constipation, pain or a new medicine, and treating it can bring the person back towards their previous level. The key is knowing the person’s baseline: what they are normally like on a good day, how they usually communicate, and what they can usually do. A sudden, fluctuating change from that baseline should prompt medical assessment rather than being accepted. Recovery from delirium can be slow – sometimes taking days to weeks after the cause is treated – and in people with dementia it may not return fully to the previous level, which is one reason prevention (good hydration, sleep, mobility, glasses and hearing aids, and avoiding unnecessary sedatives) matters so much. After an episode, it’s sensible to have memory and thinking reviewed once the person has recovered, and to note the episode – and what seemed to trigger it – in case it happens again, which can help prevent or catch the next one sooner.

When to seek urgent care

Any sudden confusion or change in alertness or behaviour in an older person should be assessed promptly – go to A&E. Some causes are life-threatening, and the earlier the trigger is treated, the better the recovery.

Sources

NHS — Sudden confusion (delirium): sudden onset, common causes, “go to A&E for sudden confusion.”
American Academy of Family Physicians (2023) — delirium in older persons: inpatient prevalence, motor subtypes, hypoactive most missed, non-drug prevention/management.
HealthHub Singapore / SingHealth — SG caregiver guidance and family-history/reorientation points.
KTPH — geriatric medicine (SG service context).

General information only. This guide is general information about the health of older adults and is not a diagnosis or personalised medical advice. See a doctor — a GP or a geriatrician — for assessment and treatment, and don’t dismiss new problems as “just old age.” Seek prompt medical care for any sudden confusion or change in alertness in an older person, and call 995 or go to A&E for a fall with severe hip or groin pain and inability to stand, or for sudden face drooping, arm weakness or speech difficulty (act F.A.S.T. — possible stroke).

Delirium (Sudden Confusion) in Singapore: A Medical Emergency