Peptic ulcer disease: This is the most common cause of upper gastrointestinal bleeding, which can manifest as hematemesis. The patient's symptoms and presentation are consistent with a bleeding peptic ulcer.

Gastroesophageal varices: These are dilated veins in the esophagus that can bleed easily, often due to liver cirrhosis. The presence of hematemesis could indicate a variceal bleed.
Mallory-Weiss syndrome: This condition involves tears in the mucous membrane or lining of the lower end of the esophagus, where it connects to the stomach. These tears can bleed, leading to hematemesis.
Gastritis: Inflammation of the stomach lining can cause bleeding, leading to hematemesis. This could be due to various factors, including alcohol use, NSAIDs, or stress.

Aortic rupture or dissection with esophageal compression: Although rare, this condition can cause hematemesis due to compression of the esophagus by the aortic pathology. Missing this diagnosis could be fatal.
Esophageal cancer: Bleeding from esophageal cancer can present as hematemesis. While less common than other causes, it's crucial not to miss this diagnosis due to its significant implications for treatment and prognosis.
Dieulafoy's lesion: A rare cause of gastrointestinal bleeding, this condition involves a small, superficial ulceration with an exposed, often large, caliber artery at its base. It can cause significant bleeding and is important not to miss.

Hemobilia: Bleeding from the biliary tree into the gastrointestinal tract can cause hematemesis. This is a rare condition, often associated with liver or biliary pathology.
Hemosuccus pancreaticus: This is a rare cause of gastrointestinal bleeding originating from the pancreas. It involves bleeding from a pancreatic duct into the gastrointestinal tract.
Angiodysplasia: These are vascular malformations in the gastrointestinal tract that can cause bleeding. They are more common in the elderly and can present with hematemesis, although they are a less common cause.