sounds like a calcium crash from inappropriate diet. take it to a vet and get some liquid calcium into him ASAP. you should switch him over to the Crested Gecko Diet if he pulls through. good luck.
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4.1 snakes, 4.3.2 crested geckos, 0.1 gargoyle gecko, 0.0.2 red-eyed tree frogs, 2.0 devon rex cats, 1.0 betta, 0.1 sun conure, 1.0 lovebird