joyfully
The prefix "un-" could be added to the word happy to create the word "unhappy," which means not happy.
shiftyly
greatful is another word for happy
As with any word, it can be used in an inappropriate manner. However, it is a legitimate word. It means happy, proud, loud, boorish, and a puffing explosion. It depends on how it is used. See the related link below for more.
The word 'how' is a questioning word, such as "How does this work?"
Solemn
Being unable to be happy means being Miserable
Healthappy (healthy and happy)
cavort
Demeanor
The word methodical is an adjective. It means in an organised manner.
The word desolate is an adjective. It means to be deserted.