be cool,you need not worry about it.
you know now that your heart is fine(after ekg) .
your problem gives some discomfort to you.
there may various causes theoritically yet
it seems there is some gastrointestinal discomfort.
due various reasons we feel dyspepsia(symptoms whats you've ,heart burn,upper abdominal discomfort
even milder form of anxiety
,sleep related problems may give rise to g.i. discomfort.
so it's common and managable thing.
you can try rantac/famocid for a week.
hope it will suffice.
if it does'nt then consult your trusted doc.