that happens to me alot also, i have a history of heart problems (svt) but after dozens of ekg's ive been told my heart now is pretty normal rythme. i asked my doctor about this, when i stand up my heart rate jumps up quickly and feels like its beating really hard.. along with walking up stairs sometimes. i was told it COULD be form inactivity being lazy sitting around for days with out any kind of exercise and stuff. but so many symptons are simialir in heart diseases its quite hard to pin point it with out proper testing. stress can also be a factor in that, but i would suggest light exercise daily, walking, stretching that kind of stuff and healthier eating habbits. and see if if lets up or gets any better, i would still suggest seeing a cardiologist though. always better safe then sorry!
I just want to add: I was diagnosed with POTS last year after six years of problems. I very rarely have dizziness or feel faint. The only symptom required for diagnosis is the drastic increase in heart rate (30 bpm or more) upon standing.
Feel free to ask questions if you have them, and best wishes.