To date, this is the best quote I have found about laughter. I begin all my programs with it:
"Laughter comes from the center of our being,
from the core of our heart.
Our belly is so full of laughter
that the laughter permeates every cell in our body.
True laughter is true prayer.
When you laugh, the whole of nature laughs with you.
It echoes and resounds and makes life worthwhile.
When things go all right, everybody can laugh.
But when things fall apart and yet you laugh,
This is evolution and growth.
Nothing in your life is more worthy than your laughter."
Sri Sri Ravi Shankar