Vertigo

Vertigo: A spellcaster with vertigo becomes dizzy and lightheaded when she casts a spell. Each time she casts a spell or uses a spell-like ability, the world spins and shifts around her. She must succeed at a caster check (with a DC equal to the 15 + twice the level of the spell being cast). If the spellcaster fails the check, she falls prone, and for 1d4 rounds takes a penalty on Acrobatics, Athletics, Ride, and Stealth checks equal to 1 + the level of the spell. While the afflicted spellcaster takes those penalties, she must also succeed at a DC 10 Acrobatics check in order to stand up from prone.

OPEN GAME LICENSE Version 1.0a - All text is Open Game Content.