It comes on over hours or days rather than months, and attention fluctuates markedly through the day. Urinary tract infections, dehydration, pain, constipation and new medications are common triggers in older adults.
People with dementia are far more likely to develop delirium, and it is often mistaken for the dementia suddenly worsening.
Why it matters
Delirium is a medical emergency with a treatable cause, and treating it can return the person to how they were the week before.
Sources
Where to check this, and where to read more. All external and all authoritative.