Delirium favors an acute onset lasting days to weeks in its subacute phase, fluctuating over time leading to disrupted sleep-wake cycle and waxing and waning level of consciousness.
Ability to attend to task is impaired as well as orientation.
Autonomic changes are common and EEGs show diffuse slow waves.
Language may be incoherent and the patient may be fearful and agitated.
Usually reversible.

Dementia is usually insidious in onset, excluding vascular dementia, which follows a stepwise connection.
Symptoms tend to be persistent and stable over time with a normalized sleep-wake cycle and normal level of consciousness in a particular patient.
Ability to attend a task is not affected, but orientation is impaired and aphasia and apathy are quite common.
Autonomic changes are unusual and EEGs, if anything, will show a mild slowing.
Rarely reversible.

Stein WM. Textbook of Palliative Medicine. London. Hodder Arnold. 2006. pp. 467-481.