I also had it in the same time frame and same age, and also had hallucinations, except mine were sounds. I still remember them! I was a pretty sick puppy. I remember lying on the sofa while our Dr came to check me out.
It’s amazing how much we remember about that flu, while being so sick, so many years ago! I still remember the odd feeling while hallucinating that I was falling, and the special taste of those lollipops!