## 4 Discussion
The absence of apneas, combined with marked nocturnal sympathetic activation and low HRV values, suggests functional dysautonomia, possibly associated with conditions such as chronic insomnia, restless legs syndrome, or even undiagnosed anxiety. Treatment aimed at improving sleep quality and regulating nocturnal autonomic activity could be hypothesized to help reduce morning hemodynamic instability and, consequently, syncopal events. Cluster B includes elderly, overweight, hypertensive women with few symptoms, moderate sleep apnea, and nocturnal desaturation. HRV shows decreased values in SDNN, RMSSD, NN50, and SDANN. The presence of cardiovascular risk factors in this group suggests a clinical profile in which syncope may be related to nocturnal bradyarrhythmic events or unrecognized intermittent hypoxia. Despite the limited daytime symptomatology, the altered HRV and nocturnal desaturation support a proactive strategy that could include treatment of sleep apnea, prolonged electrocardiographic monitoring, and potential evaluation for pacemaker implantation if an arrhythmic cause of syncope is confirmed. Cluster C represents older men, mostly former smokers, who are asymptomatic, with mild sleep apnea. HRV does not reveal significant alterations. This group represents a low-risk phenotype, in which the likelihood of syncope related to sleep apnea or dysautonomia is minimal. In this context, expectant clinical follow-up and education on warning signs may be sufficient, reserving invasive or costly complementary tests only in the event of recurrence. Cluster D is characterized by obese men with hypertension and dyslipidemia, presenting with severe sleep apnea and a central component. They exhibit abnormal HRV patterns, likely influenced by the use of negative inotropic agents [48]. This group may benefit from intensive intervention, which should include treatment of sleep apnea with CPAP, strict control of cardiovascular risk factors, and electrophysiological evaluation. nocturnal autonomic dysfunction and sustained hypoxia may act as triggers for bradyarrhythmias or sinus pauses, making the combination of polygraphy and overnight Holter monitoring a potentially valuable strategy to identify these mechanisms. The presence of symptomatic SA supports the indication for treatment and subsequent clinical follow-up to assess the potential reduction in syncope. Cluster E includes young men and women who are active smokers, with poor sleep quality, fatigue, daytime sleepiness, mild or absent apnea, and moderate desaturation. High nocturnal sympathetic activity may represent an early or subclinical form of dysautonomia related to poor sleep hygiene and harmful habits. Despite presenting only mild apnea, the HRV pattern, along with both daytime and nighttime symptoms, points to nocturnal autonomic nervous system dysfunction with potential impact on clinical stability. This group could be considered for non-pharmacological interventions focused on improving sleep hygiene, smoking cessation, and stress management. Nevertheless, high nocturnal sympathetic activity suggests that addressing nocturnal events may help improve HRV and reduce the frequency of syncope episodes. Taken together, the identification of these five clinical profiles not only highlights the heterogeneity of SUC but also allows, for the first time, the proposal of differentiated management strategies based on routine clinical data and non-invasive studies, although these proposals remain exploratory and require further validation. Thus, the use of artificial intelligence tools, combined with polygraphy and HRV, could be integrated into clinical decision-making algorithms to guide the rational use of diagnostic resources, prioritize treatments, and reduce diagnostic uncertainty in this complex group of patients. The finding of increased nocturnal sympathetic activity in patients with sleep apnea [49] supports the hypothesis that treatment with CPAP may improve nocturnal HRV [50] and thus stabilize daytime ANS activity.