Answer
Antonio obviously had an enjoyable meal, but he ate too much of rich not-so-healthy foods. All that coffee and the smoking and the alcohol soon after eating did nothing to calm his autonomic nervous system. By lying down so early after eating, he partly neutralized the help of his one ally (gravity), and his lower gastroesophageal sphincter ( cardiac sphincter) could not hold against the pressure of the mixing food in the stomach. When the sphincter gave way against the pressure from below, some of the acidified chyme rushed into his lower esophagus and irritated the lining. This was the cause of the substernal pain. Stomach chyme becomes very acid (pH 1-2) during the early part of gastric phase of digestion, but the layers of stomach mucus protects the stomach epithelium. The esophagus has no such protection, and so is easily damaged by acidic substances.
Work Step by Step
Antonio did well to call 911, nevertheless. With chest pains one cannot be too sure. To quote an adage appropriate for this case, "It [was] better to be safe than sorry."
