What Causes Low Potassium And Magnesium Levels?

I have several questions. My 65 y/o mother is currently in hospital. hx of diabetes, cardiac bypass x5, lymphcytic colitis, hx replacement x 3weeks. She has had three bouts of potassium and magnesium bottoming out. We would like to know what causes these to drop. this past episode here potassium went to 8 and had to have to rounds of dialysis. now bloodpressure up , blood sugars out of control, two units of blood. and several bags of magnesium and potassium after dialysis. help need to understand why and what we can do to keep her from crashing again. she goes alter mental when dropping.what kind of questions should we be asking her doctors?