Source: Dragon #328
You become fatigued when your body is assaulted by poison or magic.
Prerequisite: Constitution 11 or lower.
Benefit: Whenever you fail a Fortitude save, you become fatigued, in addition to any other effects you might suffer. This condition lasts until you get 8 hours of complete rest. This flaw applies only once to any given source that requires a Fortitude save. Failing a Fortitude save while fatigued causes you to become exhausted.