Do you not think you will be stressed on board an aircraft carrying 200+ people?!?!?.
Lots of people suffer from palpitations, a lot of the time it is nothing to worry about, and to be honest its hard for the doctors to actualy record this. (I had a few 24 hour monitors, which recorded nothing). However if you say it occurs during stressful situations, i would keep that bit under your hat, as this would no doubt put you in a dodgy situation with the airlines and with the cardiologist.
If you mention to the medical examiner you have these problems, you will probably be referred to a cardiologist.