There is something called vestibular syndrome that will mimic a stroke. Strokes are rare in dogs but they do happen. Fortunately they don't affect dogs as they do people and recovery should be made in a few weeks. Vestibular disease is when the inner ear and brain do not communicate which puts the dog off balance. You may notice a head tilt to one side or rapid eye movement also. Vestibular disease can be caused by an ear infection or other eat problem or it can be idiopathic. Generally idiopathic vestibular occurs in older dogs. I would bring the dog in for a check up of the ears. I am going to direct you to sites on both strokes and vestibular disease for further reading.