When I say Heidegger is humorless, I also mean that his notion that Da-sein has moods is limited to very dark and depressing and anxious moods, because, after all, the foundation of Da-sein is a great abyss. There is no laughter, and hence no pleasure in knowledge in his work, in his existential moods. In great part, the angst arises out of the realization that man is in the condition of “falleneness” and man has been existing already from primordial times to be in “thrownness,” although I like to think of it that as Heideggerian Being has excreted Da-sein.Being and Time is not primarily about moods and is certainly not a catalog of moods, but only uses certain moods to illustrate. On the other hand, its treatment of some moods is probably its greatest influence. European literature and other arts were never the same after it, and its imitators, but it's hard to say what its influence on philosophy will be in the long term.
About this bad mood, Leo Strauss writes: “Existentialism appeals to a certain experience, anguish or angst, as the basic experience in the light of which everything must be understood. Having this experience is one thing; regarding it as the basic experience is another thing. That is, its basic character is not guaranteed by the experience itself. It is only guaranteed by argument.” I assume that Strauss intimates that if the experience itself were enough, there is no real need to write the argument of Being and Time.