Hello I am 61 yrs old and I been using metoprolol tartrate 25 mgs twice daily and I been noticed I feel funny when I been working on gardening greenhouse and feel weak and I check my blood pressure its normal but heart rate low avgs like 50 sometime later on normal mostly low heart beating what cause it ?? Should have to be cut down once daily instead twice daily just wondering my appt Dr next week pls reply thank you ...