You should be concerned now
Thanks for the query to H.C.M. Forum.
You are taking beta blockers 80 mg twice in a day.
Heart beat is 48 / minute.
At the age of 51 years , slow heart beat with lightheadedness
is concerning .The slow heart beat is an indication of heart failure
.You need to investigated with E K G (Electrocardiogram) & echocardiogram
to isolate the case . I would recommend you visit a cardiologist at the earliest and sort this problem. Please don't wait , light headedness subsides itself.
Hope this information will help you. If further any question I will help. Good luck Dr. HET.