This has happened to me in the past. Patience and time are the only real cures.
There are a few things that could have triggered this:
If you order your frozen prey in bulk and recently switched suppliers this could have caused your problems. The scent of the prey can be altered in a number of ways and this can throw a picky python's senses into a temper tantrum. Different rodent breeders will sometimes use different bedding, different feed, even the various packing methods can change the scent of the end product. Even individual rodent colonies will have their own unique scent They may all smell the same to us (bad!), but as far as your python or other rodents are concerned the difference can be huge.
There is also the issue of freshness. If you haven't recently ordered a new shipment of rats the ones you have could be getting old. They still can "go bad" in your freezer. Freezers do not stop decay, they only slow it down. Of course, the supplier you used could have sent you an old batch also (or maybe a new batch... some of my snakes prefer a little "rankness" on their rats and won't touch the fresh killed frozen prey).
If you purchase your frozen rats from a pet store they could have encountered any number of the variations outlined above. Even though they may still be offering you a quality product they may have switched breeders or the breeder may have switched feed or bedding at their facility. A lot of variables can be introduced between the rat tub and your snake's rack that can affect how appetizing a limp, re-heated rodent appears to your python.
Of course, this is all assuming you have not altered your snake's environment in any way that could have triggered his fast. New hide, different bedding, water dish, bigger (or smaller) tub (or tank), relocating the tank to another room, moving to another house, temperature, etc.