If all your cardiac investigations are normal then it could be due to hyperacidity or Gastro oesophageal reflux disease where undigested food comes in throat and causes this sort of complaint.
In ayurveda we offer avipatikar churan 500mg mixed with shankh bhasam along with tab. soot shekhar ras 2 bd. one hour after meals
Dr. Rajesh Lakhanpaul

I can under stand your anxiety and confusion, relax.If all of your reports for cardiac work up are normal you should not be worried, what else you can have is reflux disease, in this the acid and food from stomach comes back to food pile when you lie down, the food pipe tissue in not used to handle this acid so it wakes you up and cause discomfort in chest. If this is the case you try following, Avoid heavy dinner, avoid high fat foods, and keep minimum time of 2.5 hours before your last meal and sleep. You can also put pillows below your mattress on head side. Try to reduce some weight if you are over weight.