Hi,
Nothing so extreme is needed at all. Just make sure your not hungover and you should be fine. If your already moderatly fit then you should have no problems with the breathing tests etc, other than that eating sensibly in the few days before is a good idea, don't eat any junk food on the day or you'll end up with huge blood sugar spike. If I'd tried to run 8 miles the day before my medical I very much doubt I would have made it there, let alone passed it. Good luck.