Dengue fever can progress rapidly from a mild illness to a life-threatening condition, and recognizing the warning signs—which typically appear 3–7 days after the first symptoms—is critical for survival. The seven most significant warning signs identified by health organizations include: 1. Severe abdominal pain or tenderness; 2. Persistent vomiting (at least three times in 24 hours); 3. Fluid accumulation (clinical signs like swelling or labored breathing); 4. Mucosal bleeding (bleeding from the nose or gums); 5. Lethargy or restlessness (sudden extreme fatigue or irritability); 6. Liver enlargement (detected by a doctor); and 7. A progressive increase in hematocrit (blood thickening) accompanied by a rapid decrease in platelet count. These "red flags" indicate that a patient may be entering the critical phase of severe dengue, where plasma leakage can lead to shock or organ failure. If any of these signs appear, immediate medical attention at an emergency department is necessary, as early intravenous fluid replacement is the primary life-saving treatment for severe cases.