Heat IllnessDr. Meirick says heatstroke is one of the many forms of heat illness. He says heat illness is a spectrum of conditions that happens when the heat in your body is rising quicker than you can rid of it. Symptoms of early heat illness include cramping in your muscles, feeling clammy, sweaty, weak and fatigued. Heat Related FactorsDr. Meirick says there are 4 heat related factors. Heat ExhaustionCramping due to heat can lead to heat exhaustion.