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Dementia guide

Dementia, depression, or delirium?

Three conditions often confused — and one of them is an emergency.

Three conditions can all cause confusion and memory trouble in older adults — and they're often mistaken for each other. Telling them apart matters, because delirium is an emergency and depression is very treatable. A person can also have more than one at the same time.

DeliriumDepressionDementia
How it startsSuddenly — hours to daysOver weeks to monthsSlowly — months to years
AttentionVery poor; drifts in and outUsually OK, but low effortUsually OK early on
Day to dayChanges hour to hour; often worse at nightOften worse in the morningFairly stable (Lewy body can fluctuate)
Memory complaintsConfused, may not noticeOften complains about memory; “I don't know”Often unaware or covers gaps
MoodFearful, agitated — or very sleepySad, flat, hopeless, withdrawnCan vary; may be anxious or apathetic
Can it get better?Usually, when the cause is treatedYes — with treatmentMost types progress; symptoms can be eased

Delirium: act quickly

Delirium is a sudden change in attention and thinking, usually triggered by an illness or a change in the body — such as an infection (a urinary tract infection is a classic cause in older adults), dehydration, surgery, new medicines, pain, constipation, or not sleeping. It's very common in hospitals.

Call the doctor the same day — or 911 if severe — if someone becomes suddenly confused, very sleepy, agitated, or starts seeing things that aren't there. Research shows delirium can speed up decline in people with dementia, so it deserves quick care.

In the hospital, you can help prevent it: bring glasses and hearing aids, keep familiar objects and a calendar nearby, help with walking early, protect night-time sleep, and stay with the person when you can.

Depression: often missed, very treatable

In older adults, depression can cause slowed thinking and poor concentration that look like dementia. Depression is also common alongside dementia, and treating it can improve daily life. Signs include sadness, loss of interest, sleep and appetite changes, and hopelessness.

Try the later-life mood check-in · Read about depression

Sources

Reviewed September 2026. Education only — not medical, legal or financial advice.