Heroic though they might be, adventurers can’t spend every hour of the day in the thick of exploration, social interaction, and combat. They need rest—time to sleep and eat, tend their wounds, refresh their minds and spirits for spellcasting, and brace themselves for further adventure.
Adventurers can take short rests in the midst of an adventuring day and a long rest at the end of an adventuring arc.
Momentum
After completing a combat encounter, each player gains a special ability called momentum. This ability can be used once to reroll the results of a d20 roll after you know the result, or to force an enemy to reroll after a successful save or successful attack against the player. You can only have once instance of momentum at a time – they do not stack.
In instances where the end of a combat encounter is not clear cut (for example, if a chase against fleeing enemies runs into their reinforcements), the DM may decide to grant momentum at the point one encounter transitions into another.
You lose any unused momentum when you take a short or long rest.
Short Rest
A short rest represents a break in the action, typically at least a couple minutes, during which characters can catch a breather and reorient themselves.
[in progress: a character can spend points from their reserves to replenish their hit points. Their vitality is also restored to its maximum value upon completion of a short rest.]
Many special abilities are restored on completion of a short rest.
Long Rest
A long rest is a period of downtime between story beats where characters can relax and restore their energy. The DM decides when you can take a long rest, which will typically be at the end of an adventure arc or during a quiet moment in the narrative. Mechanically, long rests are used by the DM as a narrative pacing tool and will often be used to represent some well-earned rest and relaxation, or to allow players to prepare themselves during the calm before the storm. The duration of a long rest is not fixed – it may cover days or months between quests, or half an hour before the enemy’s forces reach the gate, whichever best suits the narrative. Players typically cannot initiate long rests themselves without completely abandoning the current quest.
At the end of a long rest, a character regains all lost hit points and reserves, in addition to gaining all the benefits of a short rest.