Gastroesophageal Reflux Disease (GERD): This condition is characterized by stomach acid frequently flowing back into the tube connecting the mouth and stomach (esophagus). This backwash (acid reflux) can irritate the lining of the esophagus, causing discomfort. The symptoms of chills, indigestion, and left upper quadrant (LUQ) discomfort could be related to GERD, especially if the patient experiences these symptoms after eating or at night.

Peptic Ulcer Disease: This includes both gastric and duodenal ulcers, which can cause indigestion and LUQ discomfort. Chills might not be a direct symptom but could occur if there's an associated infection.
Gastritis: Inflammation of the stomach lining can lead to indigestion, discomfort, and potentially chills if caused by an infectious agent.
Functional Dyspepsia: A term for recurring signs and symptoms of indigestion that have no obvious cause. Chills might be less commonly associated but could be part of a broader symptom complex.

Myocardial Infarction: Although typically presenting with chest pain, some myocardial infarctions can manifest atypically, especially in women, with symptoms such as indigestion or discomfort that might be mistaken for gastrointestinal issues. The presence of chills could indicate a systemic response to stress or pain.
Pulmonary Embolism: Can present with sudden onset of chest pain and might be accompanied by chills due to systemic stress or associated infection. The pain can sometimes be referred to the LUQ.
Sepsis: An overwhelming infection that can cause a wide range of symptoms including chills, and if the source of sepsis is intra-abdominal (e.g., a perforated ulcer), it could cause LUQ discomfort.

Pancreatitis: Inflammation of the pancreas, which can cause severe abdominal pain, often in the upper abdomen, and might radiate to the back. Chills could be present if there's an infectious component.
Splenic Infarction or Abscess: Given the location of the spleen in the LUQ, conditions affecting it could cause localized discomfort. Chills could be present due to an infectious or inflammatory process.
Esophageal Spasm or Rupture: These are less common conditions that could cause chest pain or discomfort and might be accompanied by chills in the case of an esophageal rupture due to the potential for mediastinitis (infection of the tissues in the mediastinum).