Sure you can leave the food in all night so long as you remove it first thing in the morning (before it starts to rot) if he doesn't eat it. Have you had him for his whole life? If he usually eats a certain way I think it's safe to say that he's not going to change his eating preferences after 10 years.
Maybe he's approaching a shed and feels like soaking a bit? When was the last time he shed?
Changing his behaviors and routines can indicate that there's a problem and I think you should definitely keep an eye on him, but at least for now none of these behaviors seem overly worrisome. If you can get a fecal sample, I'd say take it in to be tested for parasites. If not, you can take him into a herp vet and have him swabbed, but that's no fun for anybody and it may not be necessary.
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