Potassium deficiency was what finally got me admitted to the hospital during my first major flare. They had to put me on a potassium drip for a couple of days, and believe me you don't want to do that if you can avoid it. Potassium is corrosive, and it hurts going in.
My main symptom was extreme weakness and fatigue. The day I went into the hospital I had to have my mother help me put on my shoes and tie them, because I was afraid if I bent over to do it myself I'd just keep going and land on the floor.