The signs exhibited by your pet is a classical presentation of heat stroke. Emergency measures should be taken otherwise your pet might collapse. Before you run to a vet, stabilize first your pet. Best measure taken is to cover your dog with a towel soaked with room-temperature water.
Showering with cold water is counter-productive and not recommended. When your pet’s body becomes too hot, it has the tendency to open up its blood vessels near the skin (peripheral vasodilation) so that blood can rush through it and bring with it the heat. When you douse your pet with cold water, normal reaction of blood vessels near the skin would be to close themselves (peripheral vasoconstriction). This stops blood from rushing to the skin and retains heat inside the body instead.
Covering your pet with a wet towel at room-temperature will not cause peripheral vasoconstriction. Peripheral vasodilation is promoted and heat transfers from the skin to the towel though the process of convection and radiation.
Pets with heat stroke usually reaches body temperatures beyond 41.1°C. Soaked towels help cool off your pet. But when temperature drops down to 39.4°C, take off the soaked towel to prevent over-cooling.