I just went through a similar thing with my male veiled. If you want, read, "Dexter's in trouble..."
Dexter had very similar symptoms, with one leg moving in a very bizarre way in relation to the others, sometimes as if he were trying to scratch himself. He had very weak and shaky movements, little or no appetite, nor desire to drink. I believe it was caused from a toxic plant he ate that was in the cage, (of course I didnt know it was toxic, if it was, until later) because one day he threw up while I was force hydrating him, and found some plant matter along with undigested crickets. I continued to force hydrate him with Pedialyte, which seemed to really help, attempting to dilute the toxin. I also took him outside for an hour or so every day to give him some sun. He has slowly improved, with a couple of setbacks. He still isnt eating like he used to, but he is eating and drinking, and pretty active.
This may or may not help, and I hope your chameleon recovers