There are probably medical sites on the internet that help identify pain/discomfort with physical issues. Like a heart attack feels like this, and a obstruct bile duct feels like that, and a kidney stone .... etc.
If you do check them out I suggest doing so from the waiting room of an urgent care facility. A close relative thought she was having food poison and went to an urgent care facility where she was diagnosed with a SCAD, a spontaneous coronary artery dissection. An emergency condition that occurs when a tear forms in a wall of a heart artery.
@samueltyler2 Please don't think A1 is any use, there is a A1 mode on my smart phone I used that mode only to have to quickly turn it off. If in any doubt go and see the Doctor of course.
Are you feeling subconsciously worried or anxious over anything? Sometimes panic or anxiety can mimic heart attack and chest pain or tightness. If you think you are completely calm, I'd see an urgent care doctor soon. There are plans and you don't want it to get to a full fledged heart attack, when it might be prevented now. I'd take an aspirin too, people are told in an actual heart event to take one because it thins the blood a small amount .
I'd get it checked out. It could be heart related. The sooner the better. I had similar things happening to me and my doctor ordered a heart monitor. I hope you get it resolved asap.
Try not to stress. Relax if you can. I know it's hard but find something soothing to listen too or whatever soothes you. Self care.
Only a doctor can diagnose and treat properly. The heartburn when laying down does sound like acid reflux/GERD for which a medication like nexium could help.
You should go to the doctor promptly though to get checked out.
"Heartburn" is a symptom of something called "acid reflux" - stomach contents coming back up into the oesophagus, and that can be controlled by over-the-counter remedies.
Otherwise you should see your doctor.
Social media sites are not the place to obtain proper medical diagnoses.
Take 2 baby aspirin first, just in case. THEN dissolve 1/2 tsp of baking soda in 6 oz of water, stir, and drink it down. You should burp up any gas trapped in there in about 5 minutes. If the pain gets better, it was gas.