I hope your treatments are going well. It isn't fun to be in the hospital but it's the place to be if something happens.
Did you see your results? How low was your potassium? Were you already supplementing with food or pills due to the diuretic?
Did they check magnesium? Why they don't do that in MGers is beyond me. They often do the basic chem panel and not the comprehensive one. Anyway, get copies of your records.
You don't necessarily have to have muscle cramping with too little or too much potassium. It depends upon how low it gets or how initially weak your muscles are. I definitely get muscles cramps from too much potassium, which hasn't happened too often throughout the years.
I hope you see an improvement from the IVIG.