What is delirium?
The sudden confusion that looks like dementia getting worse overnight, and needs a doctor's attention.
Delirium is a sudden change in attention and thinking that develops over hours to a few days and tends to come and go during the day. It is usually triggered by a medical problem such as infection, dehydration, a new medicine or surgery. It is common in people with dementia and is a reason to contact a doctor promptly.
What it looks like day to day
Yesterday your father was his usual self; today he cannot follow a sentence, insists it is 1985, and is picking at the air.
Or the opposite: your mother, normally chatty, is drowsy, dazed and barely eating. Mayo Clinic describes hyperactive delirium (restless, agitated, sometimes seeing things), hypoactive delirium (sluggish, withdrawn, easy to miss) and mixed forms that swing between the two. Sleep often flips, with nights awake and days asleep.
Why it happens
Delirium is the brain reacting to stress elsewhere in the body. Common triggers listed by Mayo Clinic include:
- Infections, especially urinary tract infections, pneumonia, flu or COVID-19
- New or changed medicines, including those for sleep, pain, allergies and mood
- Dehydration, low sodium or poor nutrition
- Surgery and anesthesia, hospital stays, pain and lack of sleep
In Florida, summer heat and reduced drinking make dehydration a real risk for older adults with dementia, who may not feel or report thirst.
Who is most at risk of delirium
Mayo Clinic lists these risk factors. A person with dementia often has several at once:
- A hospital stay, especially after surgery or in intensive care
- Living in a long-term care facility
- Dementia, stroke or Parkinson’s disease
- A past episode of delirium
- Vision or hearing loss
- Several medical conditions at once
Mayo also notes that symptoms often worsen at night and in unfamiliar places, which is why a hospital room can tip a fragile person over.
Seven signs to act on the same day
- Cannot hold attention or follow a short conversation.
- Suddenly much sleepier, or much more restless, than usual.
- Seeing or hearing things that are not there.
- New trouble speaking, reading or understanding.
- Sleep flips from night to day.
- Confusion that comes and goes over the day.
- Any of the above with fever, a fall or a new medicine.
Write down when each sign started. Clinicians use the timeline to separate delirium from slower changes.
When to call the doctor
Treat sudden confusion as urgent. Contact your loved one’s doctor the same day, especially with fever, cough, burning urination, a recent fall or a new medicine. Call 911 for trouble breathing, chest pain, unresponsiveness or signs of stroke. Bring a description of your loved one’s usual abilities; Mayo Clinic notes this helps clinicians recognize the change. Our post on spotting UTIs, infections and delirium in dementia walks through the warning signs.
What helps at home and in the hospital
- Keep fluids going and offer drinks every hour or so.
- Keep glasses and hearing aids on, a clock and calendar visible, and lights on during the day.
- Protect sleep at night: dim lights, little noise.
- Stay with your loved one in the hospital when you can; familiar voices calm.
- Ask the care team before giving over-the-counter sleep aids containing diphenhydramine.
Our hospital survival guide and hospital information sheet help with that.
Delirium vs. dementia (and sundowning)
| Delirium | Dementia | |
|---|---|---|
| Onset | Hours to days | Months to years |
| Attention | Badly impaired | Usually alert early on |
| Course | Swings through the day | Fairly steady |
| Reversible? | Often, once the cause is treated | Generally progressive |
Sundowning follows a late-day pattern that builds over time; delirium is a sudden break from your loved one’s baseline at any hour.
What recovery can look like
Mayo Clinic says an episode can last a few hours or stretch to weeks or months, and treating the cause usually shortens it. People with dementia may not return fully to their earlier level, so give the doctor your own description of the “new normal” after a few weeks. Mayo also advises waiting until delirium has cleared before any memory testing, because results taken during an episode can be misleading.
Keep the hospital information sheet filled in before the next emergency, and track daily changes after discharge in the printable care log.
After an episode
Recovery can take days to weeks. Extra supervision during that time lowers the risk of falls and readmission. Families often add short-term companion visits after a hospital stay; see our page on care after hospital discharge.
Related terms
Extra eyes during recovery
Companion visits after a hospital stay to help with fluids, routine and calm. 3-5 profiles in 48 hours, $35/hour for 40+ hours a week.
Frequently asked questions
Still have questions?
Talk it through with us. A free call about your family's situation, with no obligation.
Call (689) 333-6079Send us a message- Screened for dementia care experience
- Florida ADRD training before the first visit
Can a UTI cause sudden confusion in someone with dementia?
Yes. Mayo Clinic lists urinary tract infections among common triggers of delirium in older adults. Call the doctor about sudden confusion.
Is delirium permanent?
Delirium often improves once the cause is treated, though recovery can take days or weeks and some people do not fully return to baseline.
How do I tell delirium from dementia getting worse?
Delirium comes on over hours or days and fluctuates; dementia changes slowly over months. Any sudden change should be checked.
Can delirium happen in the hospital?
Yes. Mayo Clinic notes hospital and intensive care stays raise the risk, especially for people with dementia.
How can you help prevent delirium in the hospital?
Mayo Clinic notes that symptoms often worsen at night and in unfamiliar places, which is why a hospital room can tip a fragile person over. Keep fluids going, keep glasses and hearing aids on, keep a clock and calendar visible with lights on during the day, and protect sleep at night with dim lights and little noise. Stay with your loved one when you can, since familiar voices calm, and ask the care team before giving over-the-counter sleep aids containing diphenhydramine. Our hospital information sheet helps too.
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