In the early stages of heat stroke, the rabbit will lay in its cage, stretched out, breathing heavy. They will often tilt their up upward and breath heavy. As heat stroke gets worse, they will become lazy and unresponsive. Sometimes they will turn blue around the nose. When this happens, they are very close to death.
If this still doesn’t work, fill up the sink and place him in room temperature water for a couple of seconds, careful to only submerge the body and not the head. Take him out and dry him off as best as you can, wrap the body in a towel tightly to dry him. If dehydration has happened in addition, you can put Gatorade in the water to provide electrolytes.