Over 9000 Experience

Never ran a game where you had to spend a few rounds focusing and gaining energy before you reached your next level. A few groups believe in training before gaining levels. You have to practice your skills before you’re competent enough to take a new level in a class. It’s a neat idea, but works best in campaigns where you’re close to a training facility. If you’re too far away, you can’t train and become stuck at your current level.

I tend to enforce a “rest” rule. You level but your abilities are not automatically recharged. You have access to the new spell slots and the like, and your maximum hit points increase, but they’re already expended until you take a rest. Depending on when in the dungeon or adventure the party gains a level, this could either be beneficial or of little consequence.