When a Spellcaster attempts to cast a spell at a level of which they have exhausted all their spell slots, they must make a Constitution Saving throw.
The DC of this saving throw is equal to 13 + The Level of the Spell cast.
On a successful save; The spell is cast.
On a failed save, the spell fails.
Regardless of the result, the Spellcaster takes a level of exhaution equal to the level of the Spell Cast.