Hi,I believe that you are suffering from stress,certain levels of stress are indeed normal but sometimes we can notice things that we otherwise would not because of it.
First of all you did not explain how you came to the conclusion of exactly how you feel that your heart is beating faster when you sleep.obviously your unconscious so how would you know?better to measure your heart rate and BP upon rising before breakfast,if your heart rate is over 100 bpm then there MAY be a problem worth talking to your doctor about.but if your heart is even 99 bpm that can be normal too.
of course cut out all caffeine based products before bedtime too.
The fact that you mention "past traumatic events"only reassures me that you are indeed in stress, which could also affect your subconscious mind when your sleeping.
What is your heart rate?
Have you had a physical by an M.D. lately?
Have you had your thyroid levels checked?