Aw, because he's a ball python. And they like to stress out new owners in particular.

How old is he? Do you happen to know his weight? (If not you might want to invest in a digital kitchen scale that can do metric units (grams) and weights from 100-3000 grams.)

My rule of thumb is, I won't freak out unless they lose 30% of their starting body weight. ESPECIALLY if the snake is a male between 400 and 800 grams. All of my juvies have hit a fast at that weight, and some of the males kept it up for several months.