You throw yourself down and play dead, you've adopted this tactic many times at the adventurer training center and it always worked!
You relax your facial muscles (although the situation is far from relaxing) and try to peek at the reaction of the Belafus(yum!): the mighty animal looks at you puzzled, brings its ugly face closer to you... but only to smell you!
It starts playing with your body by tapping you with its paw (as big as a billiard table) making you roll back and forth in the room.
As it plays with you it takes great courage, skill and remarkable professionalism to control the nausea that builds in you.
Luckily the monster soon gets tired of you and starts sleeping in the corner!
This is a good time to escape!