leopard geckos need a hotspot of around 92* so I would try to bump that up a little bit.

To be honest with you, my male did this when I first got him too. Just try leaving the tank alone except to add water or spot clean for a day or two and he should go back to normal. if he doesn't then I would be worried more.

And I'm sure you've heard the sand debate about leopard geckos hundreds of times, and I'm not going to tell you what to do with your tank. But ceramic tiles from a hardware store work GREAT with leopard geckos and are much easier to clean than sand. I've been using them for 3 years and have never had a problem.

good luck, I hope he gets better.