As of a few weeks ago, I have constant sinus tachycardia mostly up to 120-125 BPM and occasionally down to 50-85 BPM.
Calling my cardiologist, he told me to the ER which I did. They monitored me for three hours, determining I didn't have AFIB (an intermittent problem for which I take blood thinners).

Blood work and chest Xrays were normal, so the ER doctor discharged me determining it wasn't necessary to hold me overnight and advising me to consult with my cardiologist. To my surprise, the cardiologist said it wasn't necessary to move my next appointment (May) up. He even said I could return to working out in the gym.

The sinus tachycardia is continuing even when I am resting as it's been going on the whole time. I read online that these symptoms translate to "inappropriate sinus tachycardia". which is abnormal and requires attention. I don't know what to do! I feel fine except for occasional slight breathlessness. There aren't many cardiologist in my rural setting (poorly medically served).