Hi, my year old male Zeus does this too. It started after he got really ill with Salmon poisoning. He had a high tempature and the vet thought it might have something to do with his blood sugar being low as he had quit eating. We were lucky enough to have a good vet who diagnosed and treated the salmon poisoning (it is very deadly) but although my handsome boy recovered, he still has the head shaking. I'm able to stop the episode by clapping my hands or calling his name or squeaking his favorite ball. I have him on a partially homemade diet. He doesn't get any processed foods and no chemicals or preservatives. The vet doesn't seem to know what the cause is and doesn't seem to be too concerned about it. Zeus is otherwise a very healthy and very active boxer boy. I would appreciate any other information anyone else has to offer. His blood tests were within normal limits, so we're stumped!!! It is so special to be able to share with all you boxer lovers!!! Thanks!!!