I had my regular ECG with my AME...fine.
A few weeks later, the letter from the CAA arrived mentioning words like 'possible cause for concern' and 'if you don't come in and see us in the next few weeks then your medical is invalid'...panic / sweating and perusal of the situations vacant pages of the local paper followed.
Saw the ECG specialist, had tests and spent ages on the treadmill. Finally told 'you're just one of those people whose Z line goes the wrong way - perfectly normal - we just had to be sure'.
I'm no Doctor, but please have faith in them, and also I have personal experience of the CAA medical department doing their best to keep a Pilot flying.
Oh - and smile...it'll make it seem better