Gastroesophageal Reflux Disease (GERD): This condition is characterized by the backflow of stomach acid into the esophagus, often causing a dull ache or pressure under the xyphoid process, especially after eating. The symptoms can be exacerbated by consuming large meals or lying down after eating, which increases pressure on the lower esophageal sphincter.

Functional Dyspepsia: This is a term for recurring signs and symptoms of indigestion that have no obvious cause. Symptoms can include pain or discomfort in the upper abdomen, which might radiate to the area under the xyphoid process, and can be triggered by eating.
Gastritis: Inflammation of the stomach lining can cause pain and discomfort in the upper abdomen, which may be perceived as pressure under the xyphoid process, especially after eating or drinking.
Peptic Ulcer Disease: Ulcers in the stomach or duodenum can cause abdominal pain that may be felt under the xyphoid process, particularly after eating or at night.

Myocardial Infarction: Although less common, cardiac issues like myocardial infarction (heart attack) can sometimes present with atypical symptoms, including epigastric discomfort or pressure that might be mistaken for gastrointestinal issues. It's crucial to consider cardiac causes, especially in patients with risk factors.
Pulmonary Embolism: Similar to myocardial infarction, pulmonary embolism can present with sudden onset of chest pain that might be referred to the epigastric area, especially if the embolism affects the lung bases.
Aortic Dissection: This is a serious condition where there is a tear in the aorta's inner layer. It can cause severe, tearing chest pain that may radiate to the abdomen, including the area under the xyphoid process.

Pancreatitis: Inflammation of the pancreas can cause severe abdominal pain, which might be felt in the upper abdomen and radiate to the back. While the pain is typically more severe and constant, it's a possibility in the differential diagnosis.
Hepatic or Splenic Pathology: Issues like liver congestion, splenic infarction, or other hepatic and splenic diseases can cause upper abdominal pain that might be perceived under the xyphoid process, though these are less common causes of such symptoms.
Diaphragmatic Irritation: Conditions affecting the diaphragm, such as diaphragmatic hernia or irritation from adjacent structures, can cause referred pain to the epigastric area, including under the xyphoid process.