Heatstroke signs and symptoms include: High body temperature. A core body temperature of 104 F (40 C) or higher, obtained with a rectal thermometer, is the main sign of heatstroke. Altered mental state or behavior. ... Alteration in sweating. ... Nausea and vomiting. ... Flushed skin. ... Rapid breathing. ... Racing heart rate. ... Headache. Jun 25, 2022