If the outer housing is cracked, the screw terminals may be visible, exposing live wires. The solution is to replace the switch. Installing replacement switches is reasonably easy.
You get voltage fluctuations if the light fixture is loose or the electrical wiring is not tight.Either the splices to the fixture must be tighter, or the fixture must be repaired or replaced.
If this happens on windy days, connections to your main electrical service wires may be loose. The loose connection may become even looser as the wires sway in the wind.
If you receive an electrical shock, the item is touching a hot wire, conducting electricity, and is not grounded. Contact an electrician to ground the item correctly and to find any loose connections.