Why we should not eat food in lying down position?

Eating while lying down is a known risk factor of developing gastroesophageal reflux disease (GERD) or heartburn around the chest area which is a syndrome where the lower esophagus does not close off properly after swallowing and allows the stomach contents such as food and acid to return back up into the esophagus through the cardiac or oesophageal sphincter, which is a ring of muscle that controls the passage of food from the throat to the stomach.

So, the best way to prevent Heartburn or GERD, we should sit while eating.