Hello."Concor"belongs to a group of drugs called beta blockers
whose main effect is the decrease in
heart rate.As you had increased heart rate
your doctor prescribed, correctly, that drug.The difference between drug doses
(2.5 vs 5 mgr) is that the highest dose produces a greater decrease
heart rate.It is important for your heart your heart rate
not high but a very low frequency can also lead to problems(
dizziness ,even
loss of consciousness).That symptoms your refers can be ,consequently, excess drug dose.
However pain in front of chest,initially,is not a result of drug dose
(except if the heart rate is excessively decreased).Pain in front of chase in his case, it is a medical emergency and ,consequently, always you have pain,you must go
to emergency service to examine you and make a urgent ecg to rule out
coronary
artery disease.
I wish you good health.
(In case the answer would have been useful please indicate this)