Heart Changing Pace :/?

Recently every now and again i have felt my heart changing pace for no apparent reason, It is not painful nor particularly detractive, for instance if I am rinding my pushbike and it happens I do not have to stop. If this could have anything to do with it i recently went to the doctor due to an enlarged lymph node,... show more Recently every now and again i have felt my heart changing pace for no apparent reason, It is not painful nor particularly detractive, for instance if I am rinding my pushbike and it happens I do not have to stop. If this could have anything to do with it i recently went to the doctor due to an enlarged lymph node, after a scan there looked to be some thyroid issues, after seeing a specialist and having a blood test it was left that all was well, I cant see this being connected because there does not seem to be anything wrong, Is the heart changing pace anything to worry about, or is it that I am being overreactive.
Update: I don't understand any of these medical websites.
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