Disturbed brain function in the context of physical or bodily illness has been recognised in the medical literature for over two millennia. The actual term delirium was not introduced until the first century AD, when Aulus Cornelius Celsus, a Roman, described it in his medical encyclopedia De Medicina. The word is thought to originate from the Latin de (meaning ‘out of’) and lira (meaning ‘furrow’). In his work, Celsus used the term delirium to describe the acute confusional states that could occur after wound infections or head injuries. However, more than 400 years before that, Hippocrates used about 16 different words to describe to the clinical syndrome that we now call delirium, with the terms lethargus and phrenitis largely consistent with the present-day concepts of hypoactive and hyperactive clinical presentations . These early descriptions emphasised the occurrence of psychosis and impaired arousal in patients with morbidity that was often distant from the brain (typically infectious). They thus include an awareness of the connection between body wellness and brain function that has been somewhat downplayed until relatively recent times with the greater recognition of the inherent connectivity of mind and body – an interface that is exemplified by the delirious state where pathology often very peripheral to the central nervous system (CNS) can cause globalised cognitive and neuropsychiatric disturbances.