I used to have some heart problems and on several occassions was sent home for several days hooked up to a portable heart monitor (called a holter monitor if you want to google it). I brought it back into the dr.'s office and he was able to download the recordings and read them for any abnormalities.
Recently, when I switched to a new medication, I've noticed my heart racing for about 20 minutes at the same time each night. This is something I'm going to bring up to my dr. when I see him next month.
And, if this helps any, I don't think a good doctor would disregard this sort of symptom. Anything with the heart should be taken seriously and given the necessary time to investigate.
I hope some of this helps - if anyting, know that you're not the only one to deal with this and that there's lots of ways to figure out why it may be happening. I wish you all the best!