Transcutaneous Vagus Nerve Stimulation on Fibromyalgia- Double-blind, Sham-controlled Randomized Clinical Trial

tVNS L is a battery-driven electrical stimulator connected to an ear electrode which is positioned over the skin of the cymba conchae. Thus, auricular vagal stimulation will be applied using the typical ear electrodes of the tVNS® L device. tVNS will be applied over the left branch for safety reasons. For sham auricular tVNS, the anodal electrode will be placed over the center of the left ear lobe. The cathode will be placed over the antitragus. This method and these stimulation parameters have been previously used for reliable blinding in other clinical studies. Series of electrical pulses with 250 μs pulse width, 25 Hz frequency, and 28 s inter-burst interval (32 sec on/28 sec off duty cycle) will be applied in each intervention session. Auricular tVNS will be applied at 1mA - 5mA intensity for 30 min per session (1 session per day, 7 consecutive days a week, 14 sessions in total)