A syndrome of orthostatic intolerance combined with excessive upright tachycardia, and usually without associated orthostatic hypotension. all variants have in common an excessively reduced venous return to the heart (central hypovolemia) while upright.

Postural orthostatic tachycardia syndrome (POTS) is a condition characterized by an abnormally large increase in heart rate upon sitting up or standing. POTS is a disorder of the autonomic nervous system that can lead to a variety of symptoms, including lightheadedness, brain fog, blurred vision, weakness, fatigue, headaches, heart palpitations, exercise intolerance, nausea, diminished concentration, tremulousness (shaking), syncope (fainting), coldness or pain in the extremities, numbness or tingling in the extremities, chest pain, and shortness of breath...