Sleeplessness Limit

A long rest is never mandatory, but going without sleep can have severe consequences. A creature can go a number of hours without sleep before they begin suffering the effects of sleep deprivation, this is called their sleeplessness limit. A character's sleeplessness limit is a number of hours equal to 24 + twice their Constitution modifier. After every 8 hour period beyond their sleeplessness limit, the character gains a level of exhaustion at the end of the eighth hour.

A long rest resets the count of hours without sleep.