Gastroesophageal Reflux Disease (GERD): This condition is characterized by stomach acid frequently flowing back into the tube connecting the mouth and stomach (esophagus). Symptoms such as nausea, indigestion, and discomfort in the left upper quadrant (LUQ) of the abdomen are common, and chills could be associated with a possible esophageal infection or irritation.

Peptic Ulcer Disease: This includes both gastric and duodenal ulcers, which can cause nausea, indigestion, and LUQ discomfort. Chills might be present if there's an associated infection.
Gastritis: Inflammation of the stomach lining can lead to nausea, vomiting, indigestion, and abdominal discomfort, including in the LUQ. Chills could be present if the gastritis is caused by an infectious agent.
Functional Dyspepsia: A condition characterized by recurring signs and symptoms of indigestion that have no obvious cause. Symptoms can include nausea, bloating, and discomfort in the upper abdomen.

Myocardial Infarction (MI): Although more commonly associated with chest pain, an MI can sometimes present with atypical symptoms such as nausea, indigestion, and LUQ discomfort, especially in women or diabetic patients. Chills could be part of a systemic response to the infarction.
Pulmonary Embolism: While typically presenting with respiratory symptoms, a pulmonary embolism can occasionally cause nausea and abdominal discomfort if it leads to acute right heart failure or if the embolism is small and affects the lung periphery, causing referred pain.
Pancreatitis: Inflammation of the pancreas can cause severe abdominal pain, often in the upper abdomen and radiating to the back, nausea, vomiting, and can be associated with chills if there's an infectious component.

Zollinger-Ellison Syndrome: A rare disorder characterized by excessive gastric acid production leading to severe peptic ulcer disease, which could explain the nausea, indigestion, and LUQ discomfort.
Eosinophilic Gastroenteritis: A rare condition where eosinophils infiltrate the gastrointestinal tract, leading to inflammation and symptoms that can include nausea, abdominal pain, and possibly chills if there's an associated infection or systemic response.
Abdominal Aortic Aneurysm: Although typically presenting with back or abdominal pain, a leaking or ruptured aneurysm can cause a variety of symptoms including nausea, and if it involves the visceral arteries, could lead to LUQ discomfort and chills due to potential embolization or infection.