 At extreme temperatures, our bodies have to work harder to keep cool, and with that comes the release of cortisol, the body's stress hormone. That can lead to the loss of sleep, which then turns into irritability. Now, some signs to look out for is heavy sweating, dizziness, a headache, and rapid heart rate. Doctors also say it's not uncommon to see more emergency room visits during excessive heat waves. You know, there's a lot of what we call insensible fluid loss.