Your dog is constantly shaking his head?

long eared dogs, as mine, can have a yeast infection which lives deep in the ear canal. dogs' ear canals are so deep that you cannot see most infections.

If there is been any type of trauma such as a fall, or worse, it could also be brain or spianl injury. You should confer with your vet to rule out any possibilites of brain or neck injuries.
http://www.divab-dogs.com

many things can cause disscomfort you should take your dog to a vet soon

even things as little as a grass seed in a dogs ear can caus problems