Dehydration means your body doesn't have enough water and fluids to function correctly, occurring when you lose more fluids than you take in, often from sweating, vomiting, diarrhea, fever, or simply not drinking enough, leading to symptoms like thirst, dark urine, fatigue, and dizziness, and can range from mild to severe. Dehydration can be caused by illness (vomiting, diarrhea, or fever), Excessive Sweating From exercise or hot weather, insufficient fluid intake (not drinking enough water), increased urination due to diabetes or certain medications (diuretics), or alcohol consumption (alcohol acts as a diuretic, increasing urine output). When dehydrated, a person may experience thirst and a dry mouth/lips; have Dark yellow, strong-smelling urine; urinate less often; feel Fatigue or tiredness; experience dizziness or lightheadedness; or have Sunken eyes or cheeks (especially in children).