During the bonk your body has run out of stored carbohydrate in the blodd, muscles and liver. There are two other sources of energy, stored fat and muscle tissue itself.
During the bonk your body is switching over to fat metabolism. It is quite possible (though unpleasant) to ride through a bonk and carry on riding for a few days depending how much fat you carry around.
The switch to muscle metabolism when you run out of fat is altogether more painful, leaving your arms and legs aching. This switch is so rare that it doesnt have a common name.