HI, I am not sure what is going on with your mom, the only thing that comes to my mind might be POTS (postoral orthostatic tachycardia syndrome) What other synptoms does she have, ? is she drinkng enough water? Does her heart rate goes up a lot(about 30 points ) when she stands up??Does she feel lightheaded when standing? Does she feel any shakiness? If she has any of this among other, ask her cardiologist about this condition, I suffer from this and these are some of my symptoms.