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“This is dangerous,” Williams says. You are in a room where the temperature is more than 100 degrees for 20-30 minutes. And then you start working out keeping your body temperature too high for longer than that. “You’re likely to overheat,” Williams adds. What follows is weakness, muscle cramps, dizziness, nausea, and headache. It’s very serious, and if you feel any of these symptoms see a doctor.