The recovery from Panic and SVT is often different and helpful.
It would be most unusual for a panic attack to end suddenly because the palpitation is due to sinus tachycardia which "winds down" gradually.
SVT stops abruptly, but the patient is not always conscious of the change in rhythm. Most of the time however the patient with SVT will recall feeling an attack or two stop instantaneously. But they often have to be asked!!