What are the dangers of putting my feet and toes in a bucket of ice water and leave them there while I sleep?

The dangers would be the same as for exposure. Freezing your feet could lead to frostbite which, depending on its severity, could require amputation. Depending on how you protected the rest of your body, you could subject yourself to hypothermia, which could lead to shock, coma, and death. While this is admittedly an extreme case, you shouldn't take the chance, in my opinion. - LJS