REN and myalgic encephalomeyelitis/chronic fatigue syndrome: Along with this vascular disturbance a unique cardiovascular situation is found in ME/CFS that is characterized by hypovolemia, preload failure, small hearts, orthostatic intolerance, postural tachycardia (POTS), chronotropic incompetence and most surprisingly a paradoxically low activity of the renin–angiotensin–aldosterone system.