I like this quote, from William Butler Yeats:

Happiness is neither virtue nor pleasure nor this thing nor that but simply growth, We are happy when we are growing.

Lately, I've suffered a bit of melancholy. Nothing serious, but just a bit overwhelming...the past year and a half has been rough - emotionally, finanically, psychologically - and sometimes I worry about being paralyzed (not physically). So the quote above is relevant. Even if in pain, if there is growth, there may be happiness.