I get these too and the way it was explained to me is that it's not actually thec heart it's the nerves and things around the heart that is actually making it feel like it's fluttering check it out to make sure but more than likely it's just going to be the nerves around the heart and above the skin that is making it feel that way

I sometimes feel as though mine is racing when in bed. I suffer with anxiety and when I thing of certain things I feel like my heart races but I wear a Fitbit and recently when I felt my heart was racing I looked at my Fitbit which measures my heartbeat and it was at a normal relaxed rate.

The normal response to pain is a increase in heart rate and BP, but it should not feel like it is racing. count your pulse for 15 seconds multipleply by 4 to check how fast it is going, also not not if it a regular beat, or early beats or skiped beats. If you have trouble breathing, jaw throat left arm or chest pain, ( exertion it can go to 100 and a regular rythym). Always mention it to your doctor as people can have bursts of a rapid heart rate some benign some need to be treated asap.they may be called spupraventricular tachycardia, atrial fibulation,[both start in the top of the heart or the atria] or ventricular tachycardia [ which is irritable ventricles beating before they are told to]. If you feel short of breath, sweaty, dizzy call you doctor as your body is telling you are in trouble.
I know I try to decern any new symptom cause and have even asked the doctor is it the fibro or something I need to pay attention to? Bursts of a rapid heart rate should be told to your doctor as he may want to do a cardiac monitor to see whre they are from and treat the cause.

Absolutely resounding yes! Just walking upstairs, despite taking Propranolol! You are not alone! It's worse when I am generally worse.

I also have anxiety and it happens to me when I have had a stressful day.