 The beginning and part of the spectrum of heat-related illness. So dehydration meaning loss of sufficient body fluid levels, right? And you can think of body water content as kind of the motor oil of the body. You need enough of it to make everything function just as it should. Dr. Bozzoli says signs of dehydration include headache, tiredness, dizziness, dry mouth, flushed skin, dark urine, and muscle cramps. In severe cases, dehydration can lead to heat stroke.