I Have High Blood Pressure And Take Metoprolol, My Cardiologist

I have high blood pressure and take Metoprolol, my cardiologist lowered my dosage to 25 MG from 50 MG this past Monday due to a low heart rate and dizziness. today my heart rate shot up to 115 BPM and bounced around most of the day. I took my medicine at 7:00 tonight and my heart rate is 76 BPM until I get active and it shoots back up to 115 BPM or more and I get dizzy. Yesterday it shot up to 122 BPM then went back down. I am very worried.