Fact. Diarrhea causes you to lose fluids. Losing too much fluid can bring on dehydration, especially in children. A child may be dehydrated if they seem thirsty, has a dry mouth or sunken soft spots on the head (infants), or is urinating less than usual or crying without tears. Adults may have similar symptoms, as well as sunken eyes and lethargy. Call your doctor if you see signs of dehydration. Your doctor may recommend drinking oral rehydration solutions, water, uncaffeinated, low-sugar sports drinks, diluted fruit juices, and broths.