One of my Border Collies collapsed when we were out for a walk back at easter and was instantly paralyzed from the midpoint of her spine back, losing all funsction in her rear end.
Following a frantic weekend and neurological exam by a specialist as Glasgow Vet School she was diagnosed with an FCE on/in her spinal cord. After some bed rest the dog was walking within a week albeit on 3 legs.
After several months of physio and using an underwater treadmill every other week, she now has full function of 3 legs and basic function in the other. I would recommend following the operation up with this if it is available to you.
At the time all we could rely on was it being an FCE as the dog was uninsured but she came around pretty quickly from bed rest which was pretty lucky, although it did involve a hands on effort to get her to do the toilet initially after loosing all function in the rear end.