Master Recuperator (5e Feat)
From D&D Wiki
Prerequisites: 15 Constitution or more
You have taken many wounds in combat, and your body has adapted to it, allowing you to recover much faster than most. You gain a pool of Con mod x Level amount of hitpoints. As a bonus action, you may draw from that pool to regenerate health. Alternatively, you may use 10 points in the pool to remove a poison or disease afflicted on you. You cannot use this pool on others. You regain 1d20 + Con points during a short rest. A long rest will completely regenerate your pool. Cannot be used while unconscious/incapacitated.