occurs about five times more frequently in females than in males. Signs and symptoms In adults, the primary manifestation is an increase in heart rate of more than 30 beats per minute within ten minutes of standing up. The resulting heart rate is typically more than 120 beats per minute. For people between ages 12 and 19, the minimum increase for a POTS diagnosis is 40 beats per minute. POTS is often accompanied by common features of orthostatic intolerance—in which symptoms that develop while upright are relieved by reclining. These orthostatic symptoms include palpitations, light-headedness, chest discomfort, shortness of breath, nausea, weakness or "heaviness" in the lower legs, blurred vision, and cognitive difficulties. Symptoms may be exacerbated with prolonged sitting, prolonged standing, alcohol, heat, exercise, or eating a large meal. Up to one-third of POTS patients experience fainting for many reasons, including but not limited to standing, physical exertion, or heat exposure. POTS patients may also experience orthostatic headaches. Some POTS patients may develop blood pooling in the extremities, characterized by a reddish-purple color of the legs and/or hands upon standing. 48% of people with POTS report chronic fatigue and 32% report sleep disturbances. Other POTS patients only exhibit the cardinal symptom of orthostatic tachycardia. Additional signs and symptoms are varied, and may include excessive sweating, lack of sweating, heat intolerance, digestive issues such as nausea, indigestion, constipation, and diarrhea, post-exertional malaise, coat-hanger pain, brain fog, and syncope or presyncope. Brain fog One of the most disabling and prevalent symptoms in POTS is "brain fog", a term used by patients to describe the cognitive difficulties they experience. In one survey of 138 POTS patients, brain fog was defined as "forgetful" (91%), "difficulty thinking" (89%), and "difficulty focusing" (88%). Other common description was "Difficulty processing what others say" (80%), Confusion (71%), Lost (64%), and "Thoughts moving too quickly" (40%). The same survey described the most common triggers of brain fog to be fatigue (91%), lack of sleep (90%), prolonged standing (87%) and dehydration (86%). Neuropsychological testing has shown that a POTS patient has reduced attention (Ruff 2&7 speed and WAIS-III digits forward), short-term memory (WAIS-III digits back), cognitive processing speed (Symbol digits modalities test) and executive function (Stroop word color and trails B). A potential cause for brain fog is a decrease in cerebral blood flow (CBF), especially in upright position. There may be a loss of neurovascular coupling and reduced