Husbandry is a great thing!

First Morelia Cheynei Spilota (AKA your jugle) is nocturnal

so the bathroom stage with all the lights is stressful and your

snake is looking for a dark place to hide. The hissing is the snake excurting as much force as it can to get to a safe spot (typical of captive snakes) all Herps choose Fight or Flight response. Please do as much research to learn about the wonderful creature you have held captive.