Delirium is a form of cognitive dysfunction that is one of the most common complications within patients who are being treated in an intensive care unit and/or experiencing a serious illness. As opposed to dementia, which involves impaired memory and gradual changes in cognitive capabilities, delirium is defined by the degree of a patient's alertness both in terms of thinking and physical movements and is typically reversible. While in ICU, many patients may go from requiring sedation for an agitated state (hyperactive delirium) to being extremely unresponsive and inactive (hypoactive delirium) – and this also occurs in ill patients in other medical settings, though somewhat less often. Contributing factors to delirium in these patients can include electrolyte imbalances, medications and/or withdrawal symptoms from certain medications, intracranial or systemic infections, dehydration, head injuries, vascular disorders and brain tumors. Treatment depends on the specific reason behind the delirium symptoms but can include exercises to keep the brain stimulated, regular sessions to re-orient the patient, ensuring that the patient follows a regular sleep schedule (without the use of sleep-inducing medications), range of motion exercises and keeping noises and other distracting stimuli away from the patient.