Dengue fever can progress to a severe form known as severe dengue, which may manifest with various danger signs. Some common danger signs include severe abdominal pain, persistent vomiting, bleeding from the nose or gums, difficulty breathing, lethargy, restlessness, organ dysfunction, and severe bleeding. These signs may indicate severe complications, such as plasma leakage, organ damage, or hemorrhage, and require immediate medical attention. It is important to be aware of these danger signs and seek prompt medical care if any of them are observed during dengue fever.