Sadness is like a silent killer. You'll know it's there and even though it won't cause you any physical pain, you'll be dying on the inside and then one day it will take over you completely till there's nothing left anymore to be happy about.
I have been there and in fact, at some point of time in their lives, everyone has or will have to. I mean I look at people around me and I see them crying over stupid things and it suddenly makes me feel as if I'm the strongest person considering the fact that I never cry, no matter what. But I have realized that every person has a different way of being sad. Of saying goodbye. Of letting go.