This is a tricky point. HRS uses a standard resting heart rate variability test to evaluate the levels of sympathetic and parasympathetic activity. According to HRV standards this test must be conducted at spontaneous breathing which should not be slower than 9 breaths per minute. Most of breathing relaxation techniques use slow breathing at about 6 breaths per minute. When you breathe at this rate a resonance occurs in baroreflex regulatory mechanism, which natural oscillations occur at this frequency. Baroreflex is involved in parasympathetic regulatory circuits affecting HR. However if we do standard HRV analysis, this oscillation (6 br/min, equivalent to 0.1 Hz) falls into LF frequency range, which is primarily associated with sympathetic regulation. Therefore it is not recommended to use resting HRV test when subject breathes slowly. You should interpret that high increase of "sympathetic" activation during slow breathing as a sign of good baroreflex.