Delirium is a sudden change in attention and awareness — developing over hours to days, fluctuating through the day — while dementia develops gradually over months to years. Delirium in an older adult is a medical emergency signal: it often points to infection, medication effects, dehydration, or another acute illness, and it is frequently reversible when the cause is treated. A person living with dementia can also develop delirium on top of it, which appears as an abrupt worsening from their usual baseline. Any sudden new confusion means call the person's clinician urgently or call emergency services — never wait to see if it passes.
Delirium and dementia can look similar but are different conditions with different urgency levels. Delirium comes on suddenly, often from an infection, medication, or other acute medical problem, and…