When should I consider visiting the vet? (losing weight, small)

[Zincubus]

Thanks everyone! I have him in a two foot, short cage. All three sides are covered (currently covering the front as well now), as well as I cover half of the top with a damp washcloth to help with humidity. He has two identical hides that he fits snugly into. I have two identical fake plants on the hot and cold side that he LOVES. There's a water bowl in the middle.

I have a UTH which I can control with temp, and a CHE with a stand. I have an AcuRite thermometer/hygrometer and I keep the ambient temp 78-85 and hot side around 91 and cold side 79 or so, which I use a temp gun to gage.

I mist when necessary.

I live in a bigger city and there are a few exotic pet vets around the area with good reviews, and even more exotic pet vets in neighboring cities, where they know about snakes! However, that would be my last resort.

I just want to gauge at what point I should be concerned enough for that.

Sounds pretty darn good to me !
The only slight thing I do differently is having the water on the cool sides - only because I've never seen any of mine drink from bowls on the warm side ... I can't abide warm water myself oddly enough