“Autonomic nervous system (ANS) dysfunction is a common feature of CFS, and can cause symptoms in virtually every organ system. Circulatory symptoms include lightheadedness, cold hands and feet and palpitations or “anxiety.” In the digestive system, autonomic dysfunction can cause nausea, cramps, constipation, diarrhea and bloating. Autonomic dysfunction can also cause abnormal breathing and urinary patterns, and problems with balance and even vision. […]”
Orthostatic intolerance (OI) refers to the inability to be vertical — sitting in a chair, or standing — without developing symptoms.
“The simple act of standing requires a complex set of interactions involving the autonomic nervous system, blood vessels, muscle and heart which work to keep the blood from draining from out of our upper body in our abdomen and/or lower body. […]”