First, you are being very honest which is good. Often people may begin to lie to themselves, and be in denial. But you are directly feeling what you are.
There is a myth in this culture which is the mental illness myth. It pretends that certain people can become 'clinically depressed' without a cause. That is absolute BS. They believe this because they believe that 'mental illness' is a biological illness. BUT in reality of course thereis always a cause. Yes the person affected may not be conscious of it---they may think that because they are 'happy' (by how this culture claims you MUST be happy, having possessions, 'success', 'great exam results'. But it is not that simple. And many people become even unconscious of how they feel. And of course they will have some tell them they are selfish to be unhappy, if they share with others. But you feel how you feel, and it is important to allow this freedom and not suppress feelings.
I agree. Most people around me show themselves as self-sufficient happy people, when deep down, they are crying over how miserable their life is. They escape through drugs, smoking, alcohol, sex, working too much, and other outlets, which is not bad if there is a purpose. What's bad is they don't want to go through it and just want to escape. I believe people really need to undergo such process in their life in order to find their true identity.