Drinking too many electrolytes can lead to an excess in potassium, which may cause muscle weakness. If the potassium excess becomes severe, it may lead to abnormal heart rhythms, and may eventually cause the heart to stop beating, according to the Merck Manual. Signs of overhydration (via sports drinks or even water) include spasms, cramps, headaches, nausea, and cloudy thinking. People with mild cases of overhydration can just stop drinking fluids for a few hours, but if a person has severe symptoms like seizures or fainting, then they need immediate medical attention (per Gundersen Health System).
That being said, overhydration is rare. For most people, getting enough fluids in the first place is a greater concern than making sure you don’t get too much. On average, men and women should get 3.7 and 2.7 liters of fluids per day respectively (per Mayo Clinic), but Gundersen Health warns against drinking more than 1 liter of fluid in an hour.