Invalid attachments. I would say he/she will be dead by this time tomorrow. I had three smooth knob-tailed geckos die in a period of about 4 months. One was about a month old (bred by me), another a young adult (bought from someone in Whyalla, SA), and my oldest female gecko I had for around 5 years. I took one to the vet for a necropsy and the cause was a bacterial infection. However I believe that the gecko purchased probably introduced the bacteria into my collection, causing my other geckos to fall ill. Similar symptoms to what you are describing. Overall weight loss, then rear legs stop working, and finally on death they look dehydrated and sunken eyeballs.
Advice from the vet was to improve my husbandry, which I have.
Good luck and if/when it dies and your still unsatisfied with people's help from here, go get an necropsy done at a reptile vet. Good luck