Sleep quality and duration are critical to cognitive, emotional and physical well-being,and poor sleep quality has been associated with an increased risk of cognitive,psychological and cardiometabolic disorders. Several important physiological activitiesoccur during sleep including a reduction in heart rate and blood pressure. In addition,sleep exerts important modulatory effects on hormone release. Previous studies have shownthat lack of sleep can generate exaggerated cortisol responses or psychological andphysiological stressors. Cortisol has widespread effects throughout the body and brain,affecting mood, arousal, energy, metabolic processes, and immune and inflammatory systemfunctioning. Therefore, disruptions in cortisol secretion during the night can influencea wide variety of processes in our body that may contribute to the perception of poorersleep quality. In addition, the salivary enzyme α-amylase is considered a biomarker ofcognitive, psychosocial, emotional or physical stress. It is important to note that theautonomic nervous system (ANS) regulates several physiological processes, including heartrate, blood pressure, respiration, and digestion. The ANS consists primarily of thesympathetic system and the parasympathetic system. Increased parasympathetic activity isconsidered to promote health, whereas a dominant or overactive sympathetic branch isconsidered to be detrimental to health.A recent study found that both sleep quality and quantity of sleep were associated withresting ANS functioning. They found that poorer sleep quality was associated with greatersympathetic dominance. Research on the sympathetic and parasympathetic branches of theANS has shown that autonomic imbalances are precursors to disease formation and otherhealth-related risks. Coronavirus disease 2019 (COVID-19), has in many cases involved thepresence of long-lasting symptoms several weeks or months after surviving acute infectionwith the virus, leading to a new disease called long COVID-19 or post-COVID-19 syndrome(PCS). A recent study showed that sleep quality influences the relationship betweensymptoms associated with sensitization and mood disorders with health-related quality oflife in people suffering from long COVID.Non-invasive neuromodulation directed to ANS may be an option to treat the sleepdisorders observed in patients with long COVID.OBJETIVES:Therefore, the primary objective of this study is to evaluate the efficacy of a treatmentprotocol on the ANS by means of non-invasive neuromodulation in aspects related to sleepin long COVID patients compared to placebo. As secondary objectives, we propose toevaluate the efficacy of a treatment protocol on the ANS by non-invasive neuromodulationin aspects related to ANS functioning, psychological variables, fatigue, pain perceptionand quality of life in patients with long COVID.