There is a very interesting discussion of moods in Being and Time. Interesting specially because it is quite different from what we generally think of when we think about moods. In so far as I understood what I read, Heidegger says that mood is not just a cognitive or psychological concept but something much more fundamental ("ontological"). He further says that there is nothing like not being in any mood. If we are in the world we are "always already in the mood."

¶ 3:46 PM