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Without a doubt, you need to get the ferret to a vet immediately, it is not fair to leave him in this condition. If he has broken his back, this is something that he will not recover from, and he really needs to be euthanased, as technically his body can carry on living, but he will be in serious pain and discomfort.
If he has suffered bruising and inflammation then your vet may discuss trying treatment such as anti-inflammatories, painkillers etc. but this should only be undertaken with the supervision of a vet to be sure that it is humane to continue.
I'm sorry to be negative, but this is absolutely not something that can be treated at home.