Hello
Thank you for your query at doctorspring.com
The symptoms that you describe cannot be attributed to salt intake. Also cocaine intake 6 yrs back is not responsible for any of them unless you had a recent go at it. was the fast heart beating present when you got the ecg done. Or had it subsided by the time you got your ecg done?
Did you measure your pulse rate when you got the feeling of increased heart rate?

From the description it looks like an attack of supraventricular tachycardia. But if the ecg was normal and you still had the sensation of increased heart rate during the ecg then probably it is all non cardiac possibly anxiety.

Still since you get these symptoms on stressful activity like sexual activity you could undergo a stress ecg to replicate the stress and see whether you have any increase in heart rate beyond normal limits. This test can also effectively answer your fear of having blockages in your heart arteries. The second test which I would like to recommend is a 24 hr holter in which a device will record your cardiac activity over 24 hours and find out if something is going wrong intermittently.
You are 27 years old. The likelihood of having a heart artery blockage at this age is extremely low. Not that young people do not get heart attacks but tye probability of you having an heart attack is very low.
I would rather suspect something like a paroxysmal supraventricular tachycardia and hence the tests that I have advised. They can rule out blockages in heart arteries as well
Regards
Dr Vivek Mahajan