Minor dehydration symptoms include thirst and dry mouth, decrease in urine, dry skin, headache, constipation and dizziness, according to Mayo Clinic. Symptoms of severe dehydration include excessive thirst and dryness, little or no urine output, sunken eyes, lost skin elasticity, low blood pressure and increased heart rate and breathing.
Mild to moderate dehydration symptoms signal the need for water or sports drinks containing electrolytes, states MedlinePlus. If severe dehydration symptoms appear, medical attention is necessary to avoid shock, unconsciousness, seizures, brain damage or death, which are all possible extreme effects of dehydration. Intravenous fluids are often used as treatment for the severe symptoms of dehydration.