First words from the Vet were "this is not good".
He said it twice after seeing my Maggie flop helplessly on the exam table. On Friday Mar 14th she had attempted to jump up to my desk top, a jump that she makes several times every day but this time she she jumped short. She fell back-wards hitting her head on hardwood floor. I was looking down at her at the time and saw how she landed and it look bad. She ran off a short ways and stumbled, her right side shoulder thereafter collapsing inward at every effort she made to stand upright. I picked her up thinking she had surely broken her collar bone or her upper leg but I couldn't detect anything broken. She didn't seem to have any pain either. It was 9 pm and I crated her with her little kitty bed and stayed up most the night observing her while waiting for the clinic to open at 7 am. We were at the clinic an hour early waiting for the first Vet to arrive. Luckily it was Maggie's Vet that arrived early and he took us in immediately. By then I didn't know it but Maggie could only flop around helplessly on the exam table on floor while softly crying. Also her head was oddly set in a position turned all the way around to the right. The Vet said after closely looking for some outward sign of trauma that she had likely suffered from severe vestibular failure to one side. Possibly not necessarily due to injury. He said he sees this condition in dogs occasionally but only one cat in his twelve years of practice. He gave her a Dexamethasone injection for the small chance there was some head swelling from injury that we couldn't see and we are back home waiting to see what develops. The Vet advised me that if she shows no improvement within 3 or 4 days that he will recommend that she see a specialist for an MRI and bulla series x-ray graphs. Maggie can neither eat or drink on her own, so I'm syringe feeding her and giving her SQ fluids. It will be 72 hours since her fall tonight and right now she seems to be mentally all there but she just can't stand up to do anything. Poor cat she seems very frightened. I have to hold her up but she does try to use her litter box.

Update March 31, Maggie's back!
The first four days were very very grim with Maggie unable to stand. She couldn't feed herself or use the litter box without my assistance. On day 5 she began to show a lot of improvement almost by the hour. She could sit up but would repeatedly fall over always to the same side but that was good considering. She was also able to crawl over to her water dish and drink but her mobility was no better than a 3 week old kitten. At the end of day 6 she became very ill, repeatedly vomiting and then had endless slimy diarrhea. I several times had to put her in the laundry tub to clean her back side which made her real mad. Finely the old Pepsid AC cleared her of the stomach upset and she has again been showing good progress with every passing day. Today I have her out of her crate and she is back on her favorite spot right in the middle of my desk. She is today eating and drinking, does just fine on her own in the litter box too. She remains a little dizzy at times and has the head tilted always to her left side. She has an odd weakness in her legs in that while she can make a low jump up she will can not come down. Today I tested her by leaving her on a chair seat and encouraged her to try to get down by herself. When she did finely come down her legs collapsed under her. I have put down nonslip pads on the hardwood floor where ever I think she could fall though. She will remain confined to the crate most of the day except when I can watch over her.