Sickened

A condition that causes a penalty to speed (~-25%), and a -2 penalty to attack rolls, damage rolls and saving throws until a successful Fortitude save is made. It generally lasts for 1-10 minutes and allows a recurring saving throw attempt every 6 seconds.

Sickened is considered a form of Poison. Thus immunity to poison will prevent this effect. It can also be removed with a Neutralize Poison spell/wand/potion.