Effect of Ondansetron on Patient Tolerance, Efficacy and Endoscopist Workload in Unsedated Endoscopy for Upper Gastrointestinal Bleeding

The goal of this clinical trial is to evaluate whether intravenous ondansetron can improve patient tolerance and reduce discomfort during unsedated emergency esophagogastroduodenoscopy (EGD). The main questions it aims to answer are: * Does pre-procedural administration of ondansetron improve patient cooperation during emergency EGD? * Does it improve endoscopic field visibility and improve the success rate of initial endoscopic hemostasis？ * Does it reduce the operator\'s perceived workload or stress? Researchers will compare patients who received intravenous ondansetron with patients who received placebo to see if ondansetron can reduce patient discomfort and improve patient cooperation, therefore improve the quality of the procedure. Participants will receive either intravenous ondansetron and dyclonine hydrochloride mucilage or intravenous saline and dyclonine hydrochloride mucilage prior to the endoscopic procedure.