Hypokalemia is a potassium level that's too low. Potassium is needed for normal bodily functions, especially for nerves and muscles. Some medications, like diuretics that cause frequent urination, can contribute to low potassium levels. Also, low potassium can be triggered by diarrhea from illness or from taking too many laxatives. Because the kidneys help keep a normal balance of potassium in the body, kidney disorders can affect potassium levels. Excess vomiting due to illness or bulimia can also cause hypokalemia.