You will have fluctuating readings from day to day depending on several environmental factors the most influential being diet.
Having had an acute episode of renal failure in the past, I can say that if you're not eating the foods that are high in potassium and not supplementing potassium, then the potassium can actually go down like that in three months. I don't think you need to really panic. All you really need to do is go see your doctor who noted the high potassium and have that doctor retest your potassium. If it has been going down like that already and you're feeling better than when it was first tested, then likely the potassium has gone down to where it should be. And, yes, within three months sounds about how quickly mine recovered.
5.3 is OK If you're that panicked then have another blood test! Unless you can't get to your doctor don't go to these urgent care facility's