Heart rate has been falling below 60 pbm lately when lying/sitting, tired much of time. thyroid test normal, is this concerning?.

Depends: You may just have a low basal heart rate. Unless you are symptomatic such as light headed or short of breath i would not make much but if having symptoms or have any family or personal history of heart problems probably at least worth getting an ekg.

Maybe: Maybe. Would be most important to know if your heart rate increases properly with exertion. Discuss this with your doctor.