You're right, why should we live as happily as possible?
But I read it somewhere that if we live with sadness, we will attract the negative vibes in our waking life, and so, many people would say that we should be happy and laugh more. You know what, happiness is a choice we can make and it is a choice that can change our life. It is within how we perceive things and react to it will bring us different kinds of emotions. And so, I don't think you are an ungrateful person because by the way you take time to heal your inner self and address your own pain is already a generous act that we can give to ourselves.