(and this fits my mood today)
Does this ever happen to you? You sit down in front of your work in progress and you're in sort of a flip mood. Suddenly you find yourself inserting puns and jokes every here and there. Little touches of humor.
Your dark story has become something else--acerbic, glib, jokey. Later, you realize you have pretty much destroyed the mood with your pitiful jokes.
Yet, maybe your humor lighten it up, providing a few minutes of joy in a joyless work. Does this happen to you or am I the only bi-polar writer out here?