When sadness overwhelms you; you feel trapped. You can do nothing to stop it, nor do you really want to stop it. If someone finds you while the sadness is consuming you, they see you happy. You smile, laugh, and put on a fake mask because you don't want anyone to know. If someone sees behind the mask, it's because you really, really want them to know, but you just don't have the words to say.
When you're alone, you aren't happy. You frown, cry, and throw your mask aside. It never gets more than arms reach away. You don't want to stop the sadness from taking over because you know it's okay to cry. It doesn't mean that you're weak, but at times, that's exactly how you feel. You almost don't mind being alone while you cry, but there's that small part of you that wants someone to comfort you.