Most people don't know about belching while laying down.
It is actually one of the worst things one can do.
Most people understand about the little gate at the top of the stomach which allows food or drink in and hopefully keeps stomach acid contained within the stomach.
When sitting or standing your body is in an upright position and the stomach fluids may be about half to 3/4 full of liquid. The remaining portion, may have air or sometimes gas at the top, so when you belch, hopefully no acid comes out with the gas.
I want everyone to think of a gallon jug of water a little more than half full.
When laying down, now the stomach becomes like water jug laying on it's side. What would happen if you took the cap off while the jug is on it's side? When you belch laying down and the little gate briefly opens to let the gas out, in many cases, stomach acid sneaks out also, causing a burning sensation, which can lead to the erosion of the esophagus or the little gate.
I Get On My Elbow