different than that of people in the general population. Other risk markers Other risk markers for fibromyalgia include premature birth, female sex, cognitive influences, primary pain disorders, multiregional pain, infectious illness, hypermobility of joints, iron deficiency and small-fiber polyneuropathy. Metal-induced allergic inflammation has also been linked with fibromyalgia, especially in response to nickel but also inorganic mercury, cadmium, and lead. Pathophysiology As of 2022, the pathophysiology of fibromyalgia has not yet been elucidated and several theories have been suggested. Nervous system Pain processing abnormalities Chronic pain can be divided into three categories. Nociceptive pain is pain caused by inflammation or damage to tissues. Neuropathic pain is pain caused by nerve damage. Nociplastic pain (or central sensitization) is less understood and is the common explanation of the pain experienced in fibromyalgia. Because the three forms of pain can overlap, fibromyalgia patients may experience nociceptive (e.g., rheumatic illnesses) and neuropathic (e.g., small fiber neuropathy) pain, in addition to nociplastic pain. Nociplastic pain (central sensitization) Fibromyalgia can be viewed as a condition of nociplastic pain. Nociplastic pain is caused by an altered function of pain-related sensory pathways in the periphery and the central nervous system, resulting in hypersensitivity. Nociplastic pain is commonly referred to as "Nociplastic pain syndrome" because it is coupled with other symptoms. These include fatigue, sleep disturbance, cognitive disturbance, hypersensitivity to environmental stimuli, anxiety, and depression. Nociplastic pain is caused by either (1) increased processing of pain stimuli or (2) decreased suppression of pain stimuli at several levels in the nervous system, or both. Neuropathic pain An alternative hypothesis to nociplastic pain views fibromyalgia as a stress-related dysautonomia with neuropathic pain features. This view highlights the role of autonomic and peripheral nociceptive nervous systems in the generation of widespread pain, fatigue, and insomnia. The description of small fiber neuropathy in a subgroup of fibromyalgia patients supports the disease neuropathic-autonomic underpinning. However, others claim that small fiber neuropathy occurs only in small groups of those with fibromyalgia. Autonomic nervous system Some suggest that fibromyalgia is caused or maintained by a decreased vagal tone, which is indicated by low levels of heart rate variability, signaling a heightened sympathetic response. Accordingly, several studies show that clinical improvement is associated with an increase in heart rate variability. Some examples of interventions that increase the heart rate variability and vagal tone are meditation, yoga, mindfulness and exercise. In 2023 the Fibromyalgia: Imbalance of Threat and