Happiness is sadness.
Joy is a state of excess, which usually refers to sadness caused by excess.
Duke Zhou: I dreamed that I was happy.
It means that you will be troubled by sadness.
Duke Zhou: The old man dreamed that he was very happy.
I will be bedridden because of overdraft.
Duke Zhou: I dreamed of the joy of my loved ones.
It means that the excessive words and deeds of relatives and friends will cause family estrangement.
Duke Zhou: Happiness in dreams, troubles outside dreams.
The vocation of life is suffering, and happiness is an escape from suffering, which is equivalent to deviating from one's vocation. So dreaming that you are happy shows that your life has deviated from the direction and will be tortured by sadness.