Daytime sleepiness in insomnia: Are we focusing on what truly matters?

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.

Profiles of Subjective Daytime Sleepiness through Cluster Analysis.

Sleepiness propensity and sleepiness perception are two relevant dimensions of the general multidimensional sleepiness construct. In the current study, the aim was to identify eventual homogeneous subgroups when sleepiness propensity and sleepiness perception measures are combined. Data from 678 undergraduate students (aged 17 to 24 years) from a medical school were analyzed. A Two-Step Cluster Analysis was performed taken into consideration sleepiness propensity and sleepiness perception measures as clustering variables. Four different clusters were identified. Additionally, the two groups comprising higher levels of sleepiness perception (i.e., "high perception, low propensity" and "high subjective daytime sleepiness" clusters) had the most compromised results in some of the sleep-related variables examined - sleep needs, sleep latency, sleep quality, sleep sufficiency, self-reported insomnia, sleep reactivity to stress, and cognitive arousal - and in some of non-sleep related variables, such as neuroticism and affect. As to non-sleep variables, those groups reported higher scores in neuroticism, arousability, self-reported mental health and affective states. The identification of distinct groups concerning self-reported sleepiness may bring new avenues for research and understanding of the specific and differential role of sleepiness and its dimensions in sleep health and sleep disturbances, in particular, insomnia disorder.