I'm not sure I'd use the word "energized". It's more like a de-stressor, or a chance to deflate a bit. It's more that when I'm around a lot of people I'm on "high-alert", and getting some time to myself lets me relax and just... be myself.
It doesn't apply to all situations - when I'm around a small number of friends and can stay pretty quiet, I do okay, chatting one-on-one I do fine, and in public places like on a bus or when I'm "on task", and can focus on what I'm doing and not anyone around me, I'm fine. But put me in any sort of high-energy social-type situation with lots of people around, and I burn out very quickly, get anxious, and start looking for an exit.