Signs of overhydration during intense exercise include excessive urination, headaches, nausea, and swelling, especially in the hands and feet, known as edema. Some individuals may experience confusion and muscle cramps due to an electrolyte imbalance. This occurs when there is an excessive intake of water that dilutes sodium levels in the bloodstream, leading to hyponatremia. It is crucial to maintain a proper balance of hydration, particularly for athletes, by monitoring fluid intake during physical activity to avoid detrimental health effects associated with overhydration.