Schematic illustration of the experimental protocol. Empty arrows indicate objective assessments and solid arrows indicate subjective assessments. Solid line with arrowhead indicate heart rate recording. Dashed lines with arrowheads indicate transcutaneous electrical nerve stimulation (TENS) treatment or simulator exposure sessions. HR, heart rate; SS, simulator sickness; VAS-SS, Visual Analogue Scales for evaluating Sleepiness Symptoms; Pre-20 and Pre-10, 20 and 10 minutes before simulator exposure, respectively; SS15 and SS30, 15 and 30 minutes after simulator exposure, respectively.