You have recently changed a piece of equipment your Wizard was wearing. Whether you got a new hat, robe, shoes, athame, ring or amulet - you have changed it out recently.
Items only boost your stats while you are wearing the item. You previously were wearing equipment that boosted your health, and have changed it out for equipment that does not boost your health as much as the old one. When you change your equipment, you will alter your stats so be aware of this in the future.
