Postural orthostatic tachycardia syndrome (POTS) is a form of dysautonomia characterized by excessive heart rate increase (greater than or equal to 30 bpm, or heart rate greater than 120 bpm, within 10 minutes of standing) without significant orthostatic hypotension, accompanied by symptoms of orthostatic intolerance (lightheadedness, palpitations, tremor, exercise intolerance, cognitive dysfunction, fatigue). The pathophysiology is heterogeneous: neuropathic POTS involves selective sympathetic denervation of the lower extremities causing venous pooling; hyperadrenergic POTS involves excessive norepinephrine release causing standing norepinephrine levels greater than 600 pg/mL; and hypovolemic POTS involves reduced plasma volume from impaired renin-aldosterone regulation. On standing, excessive venous pooling in the lower extremities reduces venous return and cardiac output, triggering compensatory tachycardia through baroreceptor-mediated sympathetic activation. POTS frequently co-occurs with Ehlers-Danlos syndrome (hypermobile joints allowing excessive venous distensibility), mast cell activation syndrome, and autoimmune conditions. The nurse performs orthostatic vital signs (supine, then standing at 1, 3, 5, and 10 minutes), educates about counter-maneuvers (leg crossing, muscle tensing, squatting), promotes volume expansion (2-3 L fluid daily, increased sodium intake 3-5 g/day), administers prescribed medications (fludrocortisone, midodrine, beta-blockers), applies compression...