Wizard's reflex is a disability found in about 25% of people with Mana in them. That means about 3.5% of the people in the WORLD have this. This forces, when a creature that has mana in them such as a Mana mass gets weakened, the affected have a uncontrollable urge to tap the mana. The people with this have a smaller Mana pool often, but also get more mana from tapping sources such as a mana attractor or a mana mass. This is caused naturally, but you can also contract it through tapping mana sources too much.
This has no side effects other than those listed.