Early autonomic dysfunction of Stage 1 (weak parasympathetic function on paced breathing and sympathetic excess on valsalva) and Stage 2 (sympathetic weakness and/or parasympathetic excess on valsalva) commonly occur without symptoms.
Symptoms begin to be felt in Stage 3 (sympathetic weakness or parasympathetic excess during a 5-minute test).
Stage 4 is associated with weak parasympathetic and/or sympathetic function are below normal during a 5-minute seated resting test. This is often referred to as low HRV (heart rate variability).
Stage 5 is an advanced state of autonomic weakness characterized by extreme parasympathetic weakness often with accompanying stronger sympathetic function, and is referred to as CAN (cardiac autonomic dysfunction).