Delirium vs. Dementia

Sudden confusion is not dementia—it may be delirium, a medical emergency. How to tell them apart and what to do.

Last reviewed: October 2026

Imagine your mother was managing well, then over two days became confused, sleepy, and convinced there were strangers in the house. That's very unlikely to be dementia. It sounds much more like delirium—a sudden change in brain function that is a medical emergency. Knowing the difference can save a life.

What is delirium?

Delirium is an acute state of confusion that develops over hours to days. It is caused by an underlying medical problem that disrupts the brain. It is very common in older adults in hospitals, especially after surgery, and is often missed. People with dementia are at much higher risk of delirium, and the two often occur together.

Key differences

	Delirium	Dementia
Onset	Sudden: hours to days	Gradual: months to years
Course	Fluctuates through the day	Slow, steady progression
Attention	Severely impaired; can't focus	Usually OK early on
Alertness	Too drowsy or too agitated	Usually normal early
Duration	Days to weeks (sometimes longer); often reversible	Long-term, progressive
Cause	An acute illness, drug or other trigger	Brain disease (e.g. Alzheimer's)

Signs of delirium

Sudden confusion or disorientation
Trouble paying attention or following a conversation
Rambling or nonsensical speech
Being unusually sleepy and hard to wake—or restless and agitated (or swinging between them)
Seeing or hearing things that aren't there; paranoia
Disrupted sleep, being awake at night
Symptoms that come and go during the day

The quiet, sleepy ("hypoactive") form is the easiest to miss—someone who is just "not themselves" and drowsy may have delirium.

Common causes

Delirium usually has one or more triggers:

Infections – urinary tract infections, pneumonia, COVID-19, sepsis
Medications – especially sedatives, sleeping pills, opioid pain medicines, anticholinergics (some allergy, bladder and stomach medicines), steroids, and drug interactions; also withdrawal from alcohol or sedatives
Dehydration, low or high blood sugar, low sodium and other chemical imbalances
Surgery and anesthesia, hospitalization, and intensive care
Pain, constipation, urinary retention
Lack of sleep, being in an unfamiliar place, and not having glasses or hearing aids
Heart attack, stroke, low oxygen, organ failure

What to do

Treat sudden confusion as an emergency. Call the doctor right away or go to the emergency department. Call 911 if the person has trouble breathing, chest pain, signs of stroke, a high fever, or can't be woken.
Tell staff what the person is normally like—"she was doing crosswords last week." Staff may not know the confusion is new.
Bring a list of all medicines, including over-the-counter drugs and supplements.

Doctors often use a quick screening tool called the Confusion Assessment Method (CAM) and look for the underlying cause with exams, blood and urine tests, and sometimes imaging.

Treatment and recovery

Treatment is aimed at the cause—for example antibiotics, fluids, or stopping a medicine. Supportive care helps the brain recover:

Familiar faces, photos and a calm voice
Glasses and hearing aids in use
Clocks and calendars; reminding gently of time and place
Daytime light and activity, a quiet dark room at night
Food, fluids and getting up and moving when safe

Medications such as antipsychotics are generally reserved for severe distress or danger. Many people recover within days, but recovery can take weeks or months, and some people—especially those with dementia—don't fully return to their previous level. Delirium is associated with faster cognitive decline, which is another reason to prevent it.

Preventing delirium

Up to a third or more of hospital delirium may be preventable. Before a planned hospital stay or surgery, ask about delirium prevention; during a stay, keep glasses and hearing aids handy, stay with the person when you can, encourage eating, drinking and walking, and ask doctors to review sedating medicines. See also Reversible Causes of Memory Problems.

Sources

Not medical advice. This article is general information, not a diagnosis or treatment plan for any individual. Talk with a doctor about your situation.

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