The Sickness unto Death is one of a few pseudonymous texts designated “psychological” by Kierkegaard: taking this designation seriously, the chapter examines what The Sickness unto Death can contribute to our understanding of moods. A promising approach taken by recent philosophical analyses of depression has focused on the concept of possibility, and has argued that possibilities are typically a feature of the world as experienced by human beings, but that a depressed person feels that possibilities are severely impoverished or utterly absent. Manic and hypomanic states tend toward the opposite extreme, of an overabundance of possibility. This chapter draws upon the resources of existential thought in order to develop an understanding of cyclothymic spectrum conditions, demonstrating how Kierkegaard’s work provides resources for a non-reductive phenomenological psychology of moods.