Symptoms of dehydration include headache, dark yellow urine, low urine output, muscle cramps, high heart rate, high body temperature, and low sweat output.(22) If you’ve been drinking lots of water but feel tired, dizzy, or achy, you might be dealing with an electrolyte imbalance and may consider supplementing your water with a sports drink or gel.(23) If your symptoms worsen or you're at all concerned with your hydration status, consult your primary physician.