The equipment that you wear on your Wizard is only giving you the bonuses while you are wearing it. You have obviously recently changed a hat, robe, athame, shoes, ring or amulet.
The previous item boosted your maximum health. When you removed the item, your health was no longer boosted.
I agree with that, Miss Greyrose, but that has happened to my life wizard and she didn't change anything. I am not sure why, and I would like a response as well.