What happens if you are over-hydrated after a strenuous exercise?

If you are overhydrated, your cells will burst. Generally, cells and the surrounding fluids are at homeostasis. If you are overhydrated, the cell's environment will be hypotonic, causing osmosis. Osmosis is the movement of solvent from an area of lower concentration to an area of higher concentration. Since at this point, there is greater concentration inside the cell, fluid will go in making the cells burst. So instead of feeling recharged, you'll feel more exhausted. It'll be better if you drink something such as juices instead of plain water so the cell's environment will not be hypotonic.