Some patients with dengue fever go on to develop
dengue hemorrhagic fever (DHF), a severe and
sometimes fatal form of the disease. Around the time
the fever begins to subside (usually 3–7 days after
symptom onset), the patient may develop warning
signs of severe disease. Warning signs include severe
abdominal pain, persistent vomiting, marked change
in temperature (from fever to hypothermia),
hemorrhagic manifestations, or change in mental
status (irritability, confusion, or obtundation). The
patient also may have early signs of shock, including
restlessness, cold clammy skin, rapid weak pulse, and
narrowing of the pulse pressure (systolic blood
pressure − diastolic blood pressure). Patients with
dengue fever should be told to return to the hospital
if they develop any of these signs.