This is mostly just a nitpick, but I can't imagine it'd be too difficult or time consuming.

Currently it feels like the spells Fullness and Satiate do the opposite of what they're described to be doing, thematically/narratively.

When you cast Fullness, you get:

Your stomach feels fuller.
You cast Fullness on yourself.
(Reducing speed of hunger gain)

When you cast Satiate, you get:

You feel less hungry.
You cast Satiate on yourself.
(Removes hunger)

I feel like the flavor text is basically backwards for the effects? That the spell that removes hunger should be Fullness, because you are actively becoming more full, and then the one that reduces hunger gain could be Satiate.

Not saying to re-balance the spells or anything, just literally swap the names/flavor text for clarity's sake.

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Less bothersome, but if the above is done, the same probably should be done for the thirst spells, too - For Consistency's Sake. Swap Hydrate (Your mouth feels less parched) to remove thirst, and Quench (You feel less thirsty) to reduce thirst gain.

It's not swapped. "Less hungry" means your hunger goes down (i.e. your hunger bar goes up). "Fuller" means your stomach stays full longer. It's not exactly an easy concept to describe in text.

However the effects now have descriptions so I imagine there won't be as much confusion.