Fever symptoms. A fever is a high temperature when the body's temperature rises above 37.5C (99.5F). The normal body temperature is between 36C-37C (96.8F-98.6F). The high temperature or fever often lasts around two to three days.Check for high temperature or fever using an appropriate thermometer and following the instructions.he normal body temperature is between 36C-37C (96.8F-98.6F). The high temperature or fever often lasts around two to three days. Check for high temperature or fever using an appropriate thermometer and following the instructions.