Long Rest

A long rest is a period of extended downtime, at least 8 hours long, during which a character sleeps or performs light activity: reading, talking, eating, or standing watch for no more than 2 hours. If the rest is interrupted by a period of strenuous activity -- at least 1 hour of walking, casting spells, or similar adventuring activity -- the characters must begin the rest again to gain any benefit from it. If the characters engage in Combat for any length of time, they must begin the rest again to gain any benefit.
On completion of a long rest, characters who have lost at least one hit point recover 1 hit point. Characters who have spent spell points recover all spell points. Characters who have at least one level of Exhaustion have the exhausted condition completely removed.
When a creature takes 3 long rests in a row (a full 24 hours of rest), on the third long rest the creature may add its Constitution modifier to the hit points regained through natural healing.