Vertigo

You cripple a target with sensations of falling. The subject of this spell becomes dizzy as the ground seems to drop away beneath its feet. The subject must succeed on a DC 10 Balance check at the start of each turn to take a move action. If it fails, it cannot move. If it fails the check by 5 or more, it falls prone. While affected, the subject also takes a -2 penalty on attack rolls and saving throws. Airborne creatures receive a +4 bonus on saves against this spell and do not need to make the Balance checks.