The idea of being happy all the time is an illusion and actually is counter-productive.
The denial of unhappiness is not healthy. The denial of ‘what is’ will lead to suffering.
Just gritting our teeth with a fake smile to the outside world and saying ‘I’m great’ when asked ‘how are you?’ is not going to do anything other than make you less happy within. The fakeness to protect the fragile ego works for a fleeting moment, but then it is gone.
Labelling ourselves within the mind as ‘unhappy’ is not good either. This is conditioning us to choose that current circumstances are bad and is setting us up to look at things in a gloomy and negative way.
If we choose to observe our current state and accept that there may be unhappiness within, then we can accept, choose to take action now, if needed, and be at peace with where we are. We are not saying that we are unhappy, we are recognising a temporary unhappiness within which we can alter now.
Denying what is, is the greatest cause of suffering within and is caused when we ignore or resist and fight our current situation or inner state. No amount of outward facade of smiling and faking will relieve the inner state, it will only worsen it by the denial.
When we accept it, then the fight subsides and peace arises. Constantly seeking happiness will make you as miserable, as it is not possible and denies unhappiness.
Philip Dodson 
So true, and as there must be dark with light there must be negative with positive. What is important is that the negative or the dark is not feared, but accepted for what it is and embraced for what it can teach us.
Definitely…the Yin and the Yang, balance