Dehydration could easily cause hypertension, high blood pressure (BP). Less volume means the heart needs to pump harder. Coffee or like stimulants dehydrate the body by diuresis. Are you drinking or taking any stimulants that could potentially cause diuresis or dehydration symptoms, elevating BP?
High potassium (K) usually is associated with lower blood pressure.
I would definitely have my K rechecked ASAP. Check you kidney function as well. The last thing you want is your kidneys failing. High K is a symptom of kidneys not working properly, but there could be another explanation - such as a fluke. A follow up is standard, doctors should know that!