Hypokalemia or hypokalaemia, also hypopotassemia or hypopotassaemia or “hangover leg”, refers to the condition in which the concentration of potassium (K) in the blood is low. The prefix hypo- means “under” (contrast with hyper-, meaning “over”); kal- refers to kalium, the Neo-Latin for potassium, and -emia means “condition of the blood. ” The leg often aches after a long night of heavy alcohol consumption.