65 Year Old Male With History Of Smoking, 6'3" And

65 year old male with history of smoking, 6'3" and 220 pounds. Active farmer. 2 1/2 years post heart attack treated with a stent in the left anterior descending artery to open a 95% blockage with no reported heart damage and was told everything else looked good. Today, went for a pre-op (knee replacement) stress test. When injected with drugs to raise blood pressure immediately heart began racing, feet began tingling, tasted chemicals, saw black spots, blood pressure plummeted, and passed out for an unknown amount of time. Came to with legs strait up in the air and was told that "you had us worried for a little while but you are okay". I was told that most people aren't affected by the drug but a few pass out. The cardiologist then left and I was not given more information. I was given an IV and fluids to drink. After a while the final chest scans were taken and I was sent home. I was and am very scared. What happened?