MBD. Metabolic Bone Disease. It's from too little Ca. Get you gecko to a vet now! I had to deal with this in my male blizzard. The vet will give a Ca injection and probally give you drops to give your little guy. Put pure Ca in a dish in your geckos' cage and dust with Ca at every feeding. Most importantly get him to a vet as soon as you can. This disease can get very bad very quickly. It can cause loss of appetite, lethargy, and permanent deformity of limbs. Luckily I caught my guys when he was shaking(just as you described) and before the lethargy/loss of appetite were too extreme. He has no deformity and is perfetly fine now. His problem was in his intestines, he does not absorb as much Ca as he should, so he needs a lot more than my other guys. Please get you gecko to a vet now.
