Inclusion Criteria: Delirious cohort  Aged 65 years and older. Documented presence of either delirium, acute confusion, or altered mental status in medical record.  Currently hospitalized with a diagnosis of one of the following:  sepsis/septicemia Pneumonia Urinary tract infection Clostridium-difficile infection  Inclusion Criteria: NON-Delirious cohort  Aged 65 years and older.  Current diagnosis of one of the following:  sepsis/septicemia Pneumonia Urinary tract infection Clostridium-difficile infection  Exclusion Criteria: all subjects  Chronic kidney disease (eGFR <30). History of Parkinson's disease. History of a major psychiatric illness. Delirium etiology of drug overdose or alcohol withdrawal. Current hyponatremia. Currently on sedative/hypnotic medications and not expected to stop. Major surgery within the past two weeks. Known or suspected Covid-19 positive.