That is classed as high, normal range is 3.5 - 5.0, Depending on your age, past medical history and symptoms is dependant on whether it needs treating or not. If you are normally fit and well then it shouldn't be a problem, if you have existing heart conditions then it can be problematic. Potassium can have an effect on the electric pathways in your heart so if your Potassium is de-arranged then you are at more risk of arrhythmia's. I work on a Coronary Care Unit and if a patient had a Potassium level of 6.2 we would treat it. My advice would be to be aware of Potassium in take, things lik 'Lo-Salt' is exteremly high in Potassium and I would advice you to go to your GP in a couple of weeks time and ask for it to be re-checked.