Marijuana addiction.

[papercuts]

If you're a chronic smoker. Stopping will cause the THC that stores in your fat to burn and enter your stream. It's a low dose, but I noticed this effect when I was in prison. I wasn't fat and was still burning fat, and it would cause a slight buzz for the first week or two.

So that's what the body is doing when you get the munchies, storing some for later, nice.