While you are subjected to the Exhausted Condition (known in older books as Exhaustion), you experience the following effects:
Levels of Exhaustion. This Condition is
cumulative. Each time you receive it, you gain
1 level of exhaustion. You die if your
exhaustion level exceeds 10.
d20 Rolls Affected. When you make a d20 Test,
you subtract your exhaustion level from the
d20 roll.
Spell Save DCs Affected. Subtract your
exhaustion level from the Spell save DC of any
Spell you cast.
Ending the Condition. Finishing a Long Rest
removes 1 of your levels of exhaustion. When
your exhaustion level reaches 0, you are no
longer Exhausted.