warbelly, as said, without more details of your general health and age, it is difficult for anyone to say much else. If you have Shortness of breath with it, it would be, more of a concern.

It concerns me, that such a low rate, makes you symptomatic--feeling tired. Do you feel that way, say if; you walked up one flight of stairs?
If so, you need to see your M.D. Many daily activities will raise our heart rate to that and most people, are unaffected. It is part of daily life. Unless, you are extremely fit. With fitness comes lower heart rates and it is more difficult to get tachycardia.

It does concern me, you are reporting that much 'tiredness' with a heart rate of about 100. Other things in your life, must do the same thing? Caffiene? many variables.

I am sativa sensitive; the stronger the sativa, the faster my heart rate. Indica's, do not have the same effect on me. However, even at 59, a pulse of 100, doesn't make me tired. pr