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.