My vet said it is called "nystagmus" and can be =
caused by a wide variety of things ..............including B vitamin =
shortage, brain tumor, inner ear defect, etc

I generally see this with head injury patients. It's usually temporary but I've
seen it last longer. Hopefully no one smacked the kitty. If he thinks it's a
vitamin deficiency, I'd most certainly give cat vitamins.

This little sweetie is grieving and tends to spend most of her time =
HIDING behind the sofa

Sounds like she has a bit of a rough past. I'd just let her hide and give her
plenty of space. Don't pick her up or approach her. Let her come to you when
she's ready. You could play with a cat toy and she may join in with you. I had
to do that with a cat I adopted that was beaten all the time. In a few months
he came around and was a sweetheart. He just needed to feel secure that I
wouldn't harm him.