I'll add the sad story of our 2 year old to this thread.
About 6 weeks ago, she began to stumble slightly. Within 2 days she was battling to walk without falling, couldn't jump and had her head tilted to the left.
The vet suspected an inner ear infection, and prescribed a course of antibiotics. At this early stage, she was not eating her normal food, but would eat her favourite mince out of my hand. Over the course of the next 10 days, she improved markedly, and by the end of the antibiotics, was walking properly, her head straight, but still couldn't jump.
Problem solved, so we thought.
A week after the antibiotics finished, she started to go downhill again with the same symptoms, but this time, her head was tilted to the right!! Her walking wasn't as bad as originally, and she was now eating her normal meals.
Back on the antiobiotics, and again she showed improvement. This time, when the ABs finished, I got another course, hoping this time to fully kill off the infection. She was back to almost normal, except that her jumping was still very restricted, and the antibiotics were still going, when she started to go backwards again, and has continued to do so, to the point where her walking is as bad as it has ever been. She continues to eat well, and will play with her toys for short periods.
The vet had mentioned from the start that a CT scan would be a possibility, but when the antibiotics seemed to be making a difference, and she was eating well (even when she was struggling) we agreed that the 4 hour round trip to the nearest scanning facility & neurologist wasn't worth the stress to her.
Now that the antibiotics have stopped working (or perhaps they never worked, and her improvements were coincidental) I've made the booking for next week, and hope that we can get to the bottom of it.
Her symptoms are not quite the same as those described by the other contributors to this thread in that she has gotten better twice, and her eyes have been normal.