My cat is back with me, and will be making an appearance again on this blog. She is fit and healthy and happy, and (I suspect) has been thoroughly spoilt by my parents.
What was wrong? I don't know, but it could have been some kind of poison she ingested recently, or poison eaten long ago, then stored in the fat cells - to re-emerge when she lost too much weight (she's fatter now!)
More worryingly, it could be some long term illness or degradation. I may never know what the problem was, but for now she seems very well.
And still determined to knock off everything on every surface of my room, before settling down at night.