You don't have to sleep in a coffin to regenerate vampire energy, but it gives you some outdoorsy-build options.
This unlocks more potent passive and activated abilities on which you can expend Power Points and enhance your Sim with new potential. Fill up the bar, and your Sim will ascend to the next level of Vampire. Each time you cross a mark on the progress bar, you'll be rewarded with points. Vampires have a rank, with a title, such as Master Vampire. There are two components to leveling up your Vampire's skills. This ensures they do not become too vampiric and balances their humanity. With each additional rank, the Vampire will grow closer to the darkness and be required to develop new weaknesses.
However, this expanding power comes with a downside. There are about 17 total levels to be gained, each of which will provide additional Power Points which allow you to select perks. As Vampires use their abilities, they gradually gain experience which is reflected in the unlocking of new Vampire Powers. Vampires in The Sims 4 gradually expand their capacity as creatures of the night and grow in strength, unlocking new perks as they progress. The Sims 4: Vampire Power Gaining Perk Points and Vampire Ranks Vampires gain experience and power points, improving their rank and expanding the selection of Vampire Powers and Weaknesses
