Did you not help him up onto branches last night or did you put him up and then he ended up at the bottom again?
If they are frightened, they might appear to fall when walking. I think it is a combination of two survival strategies--fleeing and bailing off a limb. When they are already on the cage floor, they can't exactly jump off a limb to the ground. Or fleeing combined with puffing up and turning sideways to appear big and fearsome to a predator.
Make sure your temps are not too hot.
Did you mist him a lot this morning and yesterday. You don't know if he was dehydrated when he was put in the box and shipped, so he needs extra care to be hydrated.