So I'm extremely introverted. To the point that sometimes I don't want anyone around me at all. That said, I force myself to be different. I have a wife and daughter. I take leadership responsibilities at my job, and plan and lead meetings that force me to be around people all day long. I try to engage small talk. These are just some examples. I do this because of how I used to re-energize myself wasn't working. I was too introverted.
What I would do when I was in college would be stay up extremely late on Friday night, sleep all day, and go to a grocery store on the opposite side of town from the college at 1am. Go grocery shopping by myself. Just walk around, and perhaps do grocery shopping if I need to. No one there. Use the automated checkout... never deal with a single person. After that, I'd go to the library on campus... it was open 24/7. I could sit in the periodicals and no one would ever come near by. I enjoyed the quiet way to much. It's not like I'd go there to play games on my laptop, or to read a book, or to think. Just to do nothing. It's wonderful. To have literally zero things to do, and zero things to interrupt you while you sit there. No distractions... just the quietness of it all.
This, in and of itself, wasn't necessarily bad. The problem was when I'd go to bed at 7am Monday morning, and miss classes. The problem was when I'd start to get drowsy in the middle of the days throughout the week because I was training myself to sleep during the daytime. At some point I just had to fight the urge to sleep in the middle of the day, and when nighttime came around I was awake and alert. Couldn't sleep if I tried. While it only took me a year to get into this habit, I'm still trying to break it.
Fortunately, with an amazing wife, I've finally got some accountability in my life, and have a purpose to be around people. I've learned that being alone isn't the best thing in the world. It is nice. Truly. But living this life alone forever would be self limiting, and perhaps the most terrible thing I could do to myself.
TL;DR: I shutdown. Or at least I used to.