Once subjects have finalized the run-in period, they are randomized to continue in 4 weeks comparative period. During this period, the control group continues with stable SoC and the active group is provided with a GammaCore® device for prophylactic and acute treatment in addition to the stable SoC Subjects stimulate 3 x 2 times daily as part of the prophylactic treatment regimen (cervical vagal nerve). Three 90 second stimulations are self-administered by the subject with 5 minutes between each stimulation on the right side of the neck.