Older cat major issues

My 15 yr old female cat has developed some major issues today and I need advice. Nimu is a very anxious cat who cannot, I repeat CANNOT go to the vet without sedation. In the past few weeks she has begun to lose weight rapidly. I have been giving her wet food and she seemed to stabilize. This afternoon she was found staring at the wall and has lost the use of her back legs. She is an indoor cat who has recently been sitting on the roof of the porch. I was waiting on the vet because she gets SOOO upset about going and I did not think she would survive the sedation. I am going to have to take her tomorrow but does anyone know what this might be? A stroke? A seizure? Surely not rabies?? She hates to be touched so I don't know for certain that she hasn't been bitten by anything, but I have not seen any marks or scratches. Any advice would be welcomed, but please don't tell me to take her to the vet. OF COURSE I am going to take her to the vet first thing in the morning. I am just wanting to hear some thoughts tonight as I sit by her. Thanks. 
 

Do she by any chance have a heart condition?  Before my cat developed fatty liver, we were watching him for signs of blood clots that were caused by HCM.  The clots will make the cats lose the use of their back legs.  You would know if that was the case because her legs would be cold to the touch.

I'm guessing by now she has been to the Vet?  What did they say?