Sweating is often absent, but the skin may be quite moist from earlier perspiration. The core temperature must be brought down immediately. In fun runs, perspiration is usually noted, and you do not need the absence of perspiration or an rectal temperature to make the diagnosis. There is usually a sinus tachycardia present, with the pulse noted to be faster than 160. The blood pressure may be low.
Liver damage is also evident when liver enzymes are measured following heatstroke.
Rapid medical attention is vital. After exercise drink more fluid than you think you need. Especially if you are over 40. Your thirst mechanism, does not appear to be as effective a gauge of your water needs as you age. Drinking fluid, while exercising and after completion will help speed your recovery.