Now you are fully aware of it. It is normal. But the more aware of it you are, the more you will be looking for it. Called focusing inwardly. You have to stop yourself from doing this. Learn how to calm yourself down. Hop onto you tube and watch a few guided relaxation videos. Learn from them and put them to use. Breathing exercises too. They all help slow that heart rate down. May take a bit of time to learn them in the right way. But well worth the effort.