My cats head keeps nodding(like Parkinson's)& she has involuntary jerks/twitches. Why could this be please?

Her nodding & twitches appear to be getting worse, causing her to unsteady on her feet. She has been nodding for about a year, but it's only in the last 3 months where it has got worse. When I took her to the Vets about 9 month ago, they said it was just old age. She is 17. She has gradually been losing weight too. She suffers stress & has had bouts of stress cystitis throughout her life. This has been getting worse as well and she has also been getting sick lots and going to the littler tray often. I had the Vet come see her & was advised she may have an overactive thyroid. She was given tablets to help calm her before I took her in to have a blood test. This worked, she calmed down & I took her to the Vets for blood tests. It was confirmed her thyroid was overactive. She was given medication to try but she started getting sickly again. She was then eating differently, like as if she had toothache, so I thought she might have a cavity too. Soon after, she wouldn't hardly eat. Then she stopped drinking. I thought she was going to die so I took her to the Vets. They said she has tarter build up so could clean her teeth & if they find any cavities, would remove the teeth. Because she was to be knocked out for this procedure I decided to have her thyroid removed. The Vets did this & had to remove both her glands as both were swollen & she did have a cavity so they removed a tooth too. I took her home to try get her to eat. I believe she was hours from death, but I nursed her constantly & force fed her through a pipette. She had 3 fits or panic attacks when I took her home from the Vets over a 5 day period too. Thankfully, 3 weeks on, she has put weight on and is improving day by day. However, she is nodding more than she used to & is twitching now. She goes to drink water and her legs really flinch for a moment. Her nodding also can make her lose her balance a bit and this is confusing her as she's not sure what's happening. Neither do I! Can anyone give a reason for this? Does she have a cats version of Parkinson's? Is her involuntary jerks & nodding due to the thyroid problem? Could she have diabetes? Could she have an inner ear problem? I'm asking here, because she is too weak to be taken back to the vets at the moment and I have searched all over the net trying to see if I could resolve her symptoms myself. Any suggestions? Thanks for your reply.