blood pressure drops

i will start with a little of my history . i have had 2 pituitary tumors. i had a craniotomy and gamma knife 2 years after. my blood pressure has been dropping and my heart races. this has been goin on for about 3 months. my bp is normally 130/90 ,,it has dropped to 110/80 and i get sick to my stomach and dizzy and feel like im gona pass out. the lowest it has dropped was 80/50 i was in my docs office and i had to lay till it came up. my doc didnt act worried and just sent me home . what could make my bp drop and should i get a second opinion ? please give me some idea why this could be happening ,,thanks