## 1 Introduction  
International Association for the Study of Pain (IASP) defines pain as \"an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in such terms\" [1]. Three dimensions are included in the current concept of pain in order to represent the different sources of modulation of the pain experience (sensory-discriminative, motivational-affective, and cognitive-evaluative) [2]. Chronic pain does not protect biological function, and it is a major part of the disease process. When symptoms last longer than 3 months, pain is considered chronic. This can occur along with other psychological symptoms, such as frequent anxiety, depression, pain catastrophizing, or fear-related movement [1; 2]. In addition, the study of pain in the field of neuroscience has given us a better understanding of different clinical entities characterized by the presence of \"nociplastic pain\", this being a recent term applied to describe the pain of patients with alterations in the nociceptive system, despite no clear evidence of actual or potential tissue damage that would lead to activation of peripheral nociceptors, nor evidence of disease or injury to the somatosensory system that would be causing the pain [3]. Emotional factors, such as anxiety and depression, and cognitive factors, such as pain catastrophizing and fear-related movement, can influence the experience of pain and are considered risk factors for pain chronification [4; 5; 6]. A complex chronic pain, in terms of the mechanisms responsible for the disease, is fibromyalgia syndrome (FMS). FMS is a highly prevalent chronic pain condition characterized by chronic widespread musculoskeletal pain as the main symptom, and is associated with the presence of tender points in multiple locations. FMS is a complex multidimensional disorder, given that patients can have other concomitant symptoms such as fatigue, unrefreshing sleep, stiffness, depression, anxiety, or cognitive dysfunction [7; 8; 9; 10; 11; 12]. Several alterations have been identified in patients with FMS in the nociceptive system (transmission, processing, and modulation of pain) [13; 14; 15; 16; 17; 18; 19]. These changes can alter the body schema. Previous research has shown that these patients suffer from more frequent falls and a lack of balance [20]. They may also perceive increased body size and decreased surrounding space during pain exacerbations, as well as deficits in tactile acuity [21; 22; 23; 24]. On the other hand, variables corresponding to the emotional-affective sphere (such as anxiety and depression) and cognitive factors (pain catastrophizing and fear-related movement) also play an important role in the pain experienced by patients with FMS. Pain catastrophizing has been associated with pain severity and disability. This construct of pain has been shown to decrease pain acceptance, which, in turn, may aggravate the symptoms of FMS [25]. Anxiety and depression have been proposed as precipitating and/or perpetuating factors of this condition and are inversely related to quality of life among FMS patients [26]. In this regard, it has been suggested that the higher the levels of pain catastrophizing, anxiety, and depression, the greater the patient's sensitivity to non-painful stimuli and difficulty in coping with the painful process [27]. In addition, fear-related movement has been reported consistently in individuals with FMS, as they show higher pain intensity and reduced physical functioning [28; 29]. These emotional and cognitive factors described above have been accentuated in recent years in patients with FMS since the health crisis of the COVID-19 disease began in 2020, as has been shown by important longitudinal epidemiological studies, translating into an exacerbation of the painful symptoms of these patients [30; 31].