A 28-year-old male with a 5-year history of duodenal bulb ulcers presents with recurrent melena and intermittent proton pump inhibitor (PPI) use. Four hours ago, he experienced hematemesis (3 episodes, ~600ml total) and melena (3 episodes, ~200g total), accompanied by marked dizziness, sweating, palpitations, and syncope upon changing from lying to sitting position.