What Causes Rapid Heart Beat And Abnormal ECG After Having Cough Syrup?

hi doc, I had taken 2 days back strong cough syrup and immediately i suffered from symptoms similar to heart attack. My heart was beating 120 pulse/min , ECG erratic but BP was normal. GP prescribed REVELOL XL 50 and I became NORMAL after 2 hours. MY QUESTION IS SHOULD i CONTINUE ? i AM QUITE NORMAL now.