Wikipedia says it better than I could.
http://en.wikipedia.org/wiki/Hyperkalemia
Wiki covers symptoms pretty well but on that they didn't mention is high potassium can cause the heart rate to decrease and even stop completely. So if you feel dizzy check your pulse and call 911 if your pulse is below 60 or lower than your normal at rest heart rate.

I presume they will be rechecking the level at intervals. I disagree with the nurse a bit when she says it can't be flushed out. Dialysis can restore potassium to normal levels but that will not be done unless the potassium is extremely high. Another way of lowering the level is by giving insulin IV and calcium choride IV and sometimes with dextrose; that method doesn't technically lower total body potassium but moves it around from your extracelluar (as in blood fluids which is what they are using to check your level)to your intracellular. There also is an enema commonly used for hyperkalemia called Kayexalate.

Did they tell you how high the level was?