idem, same age, also sportive (and vegetarian). Did you finally find where it comes from?
I would say that you should definately talk to your doc about it......perhaps he can do an EKG and/or holter monitor. I am 37 too and my husband has lost a few friends in the past few years that died from sudden cardiac death, when they too were in what was thought as "excellent shape". My dad had a quad bipass at the age of 54 which was followed by several more heart attacks, which was followed by a brain stem stroke. he too was in very good health (outside of high BP....non-smoker, etc), but his was heriditary (his dad passed away from a hidden blockage that ruptured and his mother passed from a stroke caused by plaque in the carodit artery).....would have happened pretty much no matter what-----BUT had he been to a doctor sooner that would have checked for blockage earlier???? Who knows.
Anyway, I'm seriously not trying to scare you, but IMHO the heart is nothing to play around with and any new/strange symptoms should always be checked out thoroughly. Every single young man that I have known that died unexpectly from a heart attack were thought of as being very healthy----who knows what "private" symptoms they were having, but brushed off thinking it was nothing. If it turns out to be nothing, great....but if there is something there....best you find out sooner than later :)