Good to hear that Sadie's a bit better. Hope to hear that she changes a 'bit' to a 'lot'.
When you first started describing what happened to her, it sounded something like what happened with Chelsea once when she was about 4-5yrs old. It was about 5-10 mins after an intense session of fetch, and she just started walking funny, stiff legged, and shaking. I seem to remember laying her down and trying to 'massage' the leg, thinking it was a muscle spasm. After about 5 mins, she was herself, but I wasn't myself. It scared the daylights out of me.
Is there anything like a clot-buster injection available, thinking back to what you describe, the spinal stroke?