After sleeping, particularly after REM sleep from what I can tell, my heart rates pretty high (in the 120 to 140) range when I stand up and walk around. Then, when I sit back down, it jumps back down to 70, but if I slightly nudge my body or something, it jumps up to 110. I assume this happens because I was in a sedentary position for so long and my body's re-adjusting? This typically goes away after 30 minutes of doing stuff.
I have had an ECG done before and the cardiologist said everything looked fine. Should I still be worried?