To establish an overarching definition of what constitutes a sleep disorder, it is essential to know which health conditions should be included in the classifications of sleep disorders and to better distinguish the normal from the pathological in sleep medicine. This would bring together several professional organizations in their understanding of this hitherto heterogeneous concept. However, no consensus regarding a general definition of a sleep disorder currently exists. We explore two of the main frameworks used in medical epistemology that could be used to define sleep disorders rigorously: harmful dysfunction analysis (HDA) and symptom network theory. For each framework, we detail the conceptual background, the method for applying it to the establishment of a general definition of a sleep disorder, the application to main sleep disorders of the ICSD-3-TR (with an emphasis on insomnia disorder) and a discussion of the main aspects of these two general definitions in the context of sleep medicine. The complementarity between the two definitions could then be considered as an “epistemic hub” which could serve to clarify the debate about what sleep disorders are, so that our understanding of them and their clinical management improve.