Dengue causes flu-like symptoms and lasts for 2-7 days. Dengue fever usually occurs after an incubation period of 4-10 days after the bite of the infected mosquito.

High Fever (40°C/ 104°F) is usually accompanied by at least two of the following symptoms:
Headaches
Pain behind eyes
Nausea, vomiting
Swollen glands
Joint, bone or muscle pains
Rash

Severe dengue
When developing into severe dengue, the critical phase takes place around 3-7 days after the first sign of illness. Temperature will decrease; this does NOT mean the person is necessarily recovering. On the other hand, special attention needs to be given to these warning signs as it could lead to severe dengue:

Severe abdominal pain
Persistent vomiting
Bleeding gums
Vomiting blood
Rapid breathing
Fatigue/ restlessness

When severe dengue is suspected, the person should be rushed to the emergency room or to the closest health care provider as it causes: Plasma leaking that may lead to shock and/or fluid accumulation with/without respiratory distress;Severe bleeding; Severe organ impairment

Courtesy of www.who.int