The Bottom Line
Reflecting on life isn't selfish, it's selfless and it helps you be a better friend.
In Detail
Reflecting on your own life isn't selfish -- in a way, it's selfless. By understanding why you do the things you do, you are able to learn the right kind of lessons you need to become a better friend, a better partner, and a better employee. So don't feel bad about wanting to spend time alone, today. Even though other people who are getting together and having fun want you to join them, your energy is much better suited to introspection. It's a good thing.