Arcane Fatigue

Conjuring magical energies is especially draining for you.
Prerequisite: Ability to cast arcane spells.
Effect: Whenever you successfully cast an arcane spell you must immediately make a Fortitude save (DC 10 + spell level). If you fail you become fatigued. If you are fatigued as a result of this flaw, it has no further effect until that condition is removed.
Suggested Class/Race: Wizard
Source:Dragon Magazine #333 (Class Acts – Flaws For Wizards)