Alcie is correct. I'd exit...stage left...from that gastro. It's typical to have reflux when lying down! It doesn't have gravity to work against. I know many have had to raise the head of their beds or raise their heads one way or another. If I have eaten something that really caused the reflux to kick in, I will have the acid come up into my mouth. Now, that's not my idea of sweet dreams! Then I'm coughing a lot because of the acid burning my throat. THAT'S when I get extra pillows to help slant my upper body up...that and 3-4 Tums usually help. If my throat still is burning and making me cough, I keep butterscotch disks in my nightstand and they are soothing and calm the burning down.
There is a link on Fibro 101 all about costochondritis. It is a muscular problem. The burning you described is what I feel with reflux. After all, the esophagus runs up behind your chest wall. You will feel it!
Don't be nervous about what they find. They might find some scarring from the acid. I have that and that's why it's important to try to keep the acid reflux to a minimum. I'm careful now that I know that can happen. Nevertheless, you do need to be checked out so you know your plan of attack. For me, I'd rather sleep through the endoscopy! Cluck, cluck, cluck! They didn't give me too much anesthesia and I woke up and actually was perfectly fine. I had no dizziness, weakness, etc. I've had three of these done and this has worked for me.
Anyway, be sure to let us know how things go for you because we really do care about you.
Sherrine