Exhausted Spellcasting

Rule Variant:

Sometimes a spell caster may be out of the spell slots needed to cast a certain spell. A spell caster has the option to use their own life force to power their spells instead of spell slots.

When a caster attempts to cast a spell without expending a spell slot, they must make a Constitution saving throw. The DC equals 10 + the spell's level. On a failure, the caster suffers a number of levels of exhuastion equal to the spell's level or 5 levels of exhaustion, whichever is higher. On a success, the caster suffers half as many levels of exhaustion, rounded up, to a minimum of 3. Regardless of a success or failure, the spell is cast.

If the spell requires concentration, the caster receives the levels of exhaustion immediately after their concentration on the spell ends.