go and get checked out by your Dr.You may just be having a slight anxiety as you are getting worried about it, but any doubt go and get checked.
You expressed everything in relative terms, "fast pace" for example, can you give a beats per minute number? If it under 100 it would not be normally be considered dangerously high. If it is 200 or similar, you should see a doctor, maybe the emergency room is in order.
Is the "pounding" only when the heart rate is up, when trying to go to sleep, or does it "pound" at other times?