This case-based session focuses on the dangerous diagnoses hiding behind common emergency department complaints. Patients with chest pain, back pain, headache, and abdominal pain often present with reassuring vital signs, normal initial testing, and plausible benign explanations. These features contribute to diagnostic error through anchoring, premature closure, and diagnostic momentum. Using real-world cases, this lecture highlights subtle clinical cues that should prompt reconsideration of the working diagnosis and outlines practical strategies to recognize high-risk conditions early, avoid cognitive traps, and initiate timely management in both resource-rich and austere environments.