Heres a little tip I came across when getting status ailments like darkness or poison. If you get it in the battle first finish the battle. Then go to your menu and then to your relics. Equip a relic that protects against the status your in and it will be gone. Then replace it with what you had before and it will not return. This is key in random battles so you do not waste items. Granted if your in a Boss battle and it is key to cure yourself then do so then. But if your exploring it will help a lot.