I've had the reflux that feels like a heart attack also. Then you start to panic, and it makes it all worse! I've had the pain in the back with it also. It is NOT FUN!
I can tell you for me that I noticed it was happening anytime I had Splenda. I am very sensitive to artificial sweeteners. Aspartame gives me migraines. I was drinking soft drinks sweetened with Splenda, and at first I thought it was the carbonation triggering it. But I can drink regular soft drinks without having the reflux pain. Drinking a lot of coffee (caffeine) will also trigger it for me.
I hope you find out what is causing your pain!