How do you know if you are dehydrated while exercising ?

Stay Hydrated: Dehydration can lead to dry mouth, thirst, headaches, dizziness, fatigue, cramping, or less coordination during exercise. Rather than look for signs of dehydration it is better to pre-hydrate in the days or hours before major exercise or a major run and to hydrate during exercise. The general rule of thumb is to drink when thirsty during exercise.

See below: You will normally become cold, clammy, feel light headed and dizzy.