Atavarr's Personal Gravitational Upset
This spell is little used and hard to master, but has the effect of swinging the victim's sense of "up" and "down" through ninety degrees. Rincewind was convinced that "down" lay at ninety degrees' variance to the conventionally accepted direction, which in practical terms meant he was confined to standing halfway up the wall until it wore off. Having been flung the length of the room and slammed into his new floor/wall with some force, he was in no position to argue about this.
Garhartra assured him there was nothing personal and he didn't enjoy doing that.