My Blood Pressure Is A Little High And I'm Pregnant?

I'm 6 months pregnant and my blood pressure has been a little high for the past 3 months. My OB doesn't seem too worried, at all. I am, though. Not only do I have heart palpitations (I've had them for years), but I'm scared that I'm going to go into cardiac arrest, or something while giving birth. I am 21 and this is my 2nd child. I'm sooo excited, but oh-so worried.