Help! Head injury or spinal injury?

Yesterday about noon, my 4 year old fell on Baby (my 1 year old female cat). I'm not sure how, I had my back turned doing the dishes. I assume he fell on her head because she immediately couldn't walk, she got extremely dizzy and finally gave up walking and laid down. I thought she was going to lay down and die, right there. Purring the whole time.

I took her to the vet to see if it was a concussion and he said it wasn't. He looked her over really good and didn't find any bruising in her eyes or anything in her ears to indicate a concussion. At that time, all I could tell him was that she was having "episodes" of dizziness. He concluded that she may have already had a tendency towards epileptic type seizures and my son's fall must have triggered it. That's all he could come up with.

The more I watch her, the more I'm convinced that it's something else. She is constantly dizzy, not nearly as bad when she's laying down as when she's standing up. Standing up, she looks like she's just learning to walk. I have to help her to get around. If she shakes her head, she falls over. It's a constant battle.

I have also come to the realization that she's not getting anything to eat. I thought she was getting a few bites down her last night, and maybe she was. But she's now not able to get the food down her throat. I can't just give her canned food because it makes her get the runs really bad, which would dehydrate her further.

I'm afraid I may have to have her put to sleep. Anybody have any idea what this might be or how to help her?
TIA Sherri