Many/some SLP have no training in actually helping to address dysfluency- and as you described, actually suggest techniques that can make the problem worse. They are trained to address articulation disorders. It’s very sad actually. I do suggest to START speaking slowly and then continue with full enunciating. Unless you have training in breathing into your abdomen, your deep breath will make everything (the panic/fear) worse. Congratulations on figuring out the truth yourself!