usually adult balls can eat a small small rat every week as there largest meal. so what might have happened is a little over feeding, and now he is going off feed to "catch up".

do you have a digital scale? i would give him a weigh, and keep monitoring to make sure he is not loosing too much weight. if he starts loosing weight, then it would be vet time. for the time being, try a smaller food item, and if he doesn't take it just leave him for the week, no handling, just changing water. a little stress free vacation might get him eating again.