Chris Coyier:

The truth about the difference between introverts and extroverts lies in how personal energy is used and gained. Introverts need a lot of recharging time to gain energy. Being out-and-about, especially in social situations, is draining. Alone time is the only way to get that energy back. For me, it’s a lot of alone time. Not sitting in a dark cave staring at the wall, but somewhere comfortable where I can do other activities I enjoy. Laying on a hotel bed catching up on the internet totally counts. At home cooking dinner totally counts. Even reading a book at a coffee shop counts.

As a socially comfortable introvert, I approve. Don’t be ashamed to go back home while your friends are going out to socialize if you need energy the next day. It’s your own psychology, and nothing to be ashamed of.