Also, it's worth mentioning again that this ailment occurred after my cat got outside one night. I finally found her and whereas one day she was fine, afterwards she has had issues with mobility in her back legs. She is clumsy in the back, unable to really jump up high anymore, and just seems to struggle all together. Sometimes it's not as bad as other times.
One thing that I've thought about that causes neurological issues is toxoplasmosis. Has anyone had any encounters with this in cats? The only reason I suggest it is because she got outside and has always been an indoor cat. If she came in contact with something that night, she may have gotten it. Any ideas?