It's entirely possible too that your doctor may want to talk to you about some anxiety medication or anything of that sort that may be the reason for the palpitations. There could be any number of reasons for your doctor wanting you to come it. It may be this doctors way of doing things as compared to your friends doctor.

I know it's so easy for our minds to go to the worst case scenario. The previous suggestion to call his office and tell them how upset you are is a good idea as well. They may be able to get you in sooner or at least to give you a bit of info that will calm you some before your scheduled appointment.

Wishing you well and please don't forget to breathe!