Insomnia, the most prevalent sleep disorder, is commonly associated with other mental and somatic disorders, making it a significant health concern. It is characterized by nighttime symptoms and daytime dysfunction, with sleepiness being a potential criterion for the latter. Sleepiness is a normal physiological state that is typically experienced near usual bedtime, in normal circumstances. In insomnia, it seems somewhat logical the idea that there is significant daytime sleepiness. However, the topic has been the subject of various discussions in sleep medicine, with studies yielding contradictory and inconsistent results. In this article, we aim to critically examine daytime sleepiness in individuals with insomnia disorder and propose an alternative approach to addressing it, both in clinical practice and research settings. It is crucial to further investigate the role of daytime sleepiness in insomnia, particularly by focusing on sleepiness perception as a more relevant dimension to explore in majority of patients. It is plausible that certain insomnia phenotypes are objectively sleepy during the day, but more studies are necessary, particularly with well-defined clinical samples. The implications of assessing sleepiness perception in insomnia for clinical practice are discussed, and new avenues for research are suggested.
Keywords: Sleepiness; assessment; sleepiness perception; sleepiness propensity; therapeutics.