To get back up after falling, you need to run and jump around a bit till you get a feeling of where you are. On one of the corners with stairs, there's a random boulder on the floor and you can actually jump on it (somewhere near it) till you find that you are elevating a bit. Stand on the same spot and keep jumping.
This only ever happens if you charge someone/get disorientated by the point between the stairs and the wall of the central platform.
They should really add some textures underneath tho to prevent this from happening. Unlike other arenas, you don't get ported back up because you're not falling.