Sometimes you DO NOT want to show your true/vulnerable colors. Depends on your work environment. For example, I was part of a truly abusive work environment several years ago, and if I had shown signs of vulnerability or emotion (anger, crying) it would have been used against me for all it was worth. In that environment, being an INFJ was a huge liability. In other environments, this isn't true.
Also - gender matters here. If you're male and you want to withdraw from time to time, that's fine. If you're female (as I suspect you, ASublett, are) then the world has even stronger expectations of you to be happy-go-lucky. There IS a lot of "pressure to perform" if you will. And it's good to be able to perform, but you have to step off the change and go out with your friends (that is, be yourself). So the right advice, in my opinion, isn't some no-holds-barred BE YOURSELF ALL PARTS OF YOU ALL THE TIME, but something more balanced -- thinking about what's situationally appropriate.
Oh, and I VERY strongly identify with your original post, ASublett. And, in response to that, this INFJ forum and just processing my visceral reactions to things with the conscious knowledge that I am an INFJ is amazingly helpful. I can talk more about that if you'd like.