Please help us, we don't know what to do.
For the past week our German Shepherd hasn't eaten but he has been drinking a lot of water. His behaviour is fine, he's active and playful but he loses weight fast. He vomitted last time we gave him raw bones. He's 6 years old. All vaccinations have been done in time. He had always had a good appetite. We've not taken him to a vet because once he attacked a vet and now we're afraid to take him there.
Ideas how to help him please?

Get a muzzle and take him to a vet as soon as possible. You have to decide which is worse: to have a couple of unfriendly growls at the vet now or to wait till his condition gets worse up to depletion when you'll have to show him to a vet anyway but it may be too late by then.