Lactic acidosis refers to lactic acid build up in the bloodstream. Lactic acid is produced when oxygen levels become low in cells within the areas of the body where metabolism takes place.The symptoms of lactic acidosis include abdominal or stomach discomfort, decreased appetite, diarrhea, fast, shallow breathing, a general feeling of discomfort, muscle pain or cramping, and unusual sleepiness, tiredness, or weakness. If you have any symptoms of lactic acidosis, get emergency medical help right away.