Try not to worry about it, especially the cost of having tests, whatever they may be!
If the ECG turns out to find something slightly irregular that doesn't mean to say the end of a career or potential career. If anything it can be useful to maintain good health.
Advise about cost: Let the NHS pay for it! If you get the good cardiologist at Gatwick you can have the ECG arranged and done the same day!
Best of luck!