Did you try flying up blindly and hoping to get close enough to the exit to transform back to human? Even if you jumped off the ledge again to take out the rest of the opponents there, you should have the first second or so clear.
Did you try lowering the resolution and all the graphics settings to see if that would help keep your framerate from dropping? I don't know if there is a way to disable the spell effects. Maybe lowering the frame rate cap would force the game to do so, or disabling HDR lighting would lower their impact, or something.
