Your dog could be having a stroke, or god knows what is the matter with him. If he were my dog, I would be at the vet as fas as I can get there.

Tick

If this is a new behaviour then he needs to be seen to by a vet.

Some dogs can be extremely nervous and back away from new objects or people but if nothing has changed around the house, and the dog has never been nervous before it could be something serious.