Does a Periaqueductal Gray-vagus Nerve Interface Malfunction Explain the Nat hx With Its Numerous Co-morbidities?

POTS sample Inclusion Criteria: * symptomatic ≥ 40 bpm rise in heart rate in the first 10 min of a tilt table study without a drop in blood pressure * Clinical symptoms of orthostatic intolerance Exclusion Criteria: * Pregnant or breastfeeding * Cognitive defects that preclude answering questionnaires or following assessment directions * Other chronic diseases * Unstable medical conditions * Use of narcotics * Limited English proficiency * Investigator discretion that participant would not be suitable to participate * A phone older than 5 years old or unable to support EMA software POST INFECTION Inclusion Criteria: * acute upper respiratory or gastrointestinal infection that required admission to the acute care units but not requiring an ICU stay Exclusion Criteria: * Pregnant or breastfeeding * Chronic prescriptions, history of POTS or orthostatic symptoms, recent inpatient psychiatric admissions, substance use disorder, trauma such as a motor vehicle accident, surgery, or other significant physical or emotional trauma in the last 5 years * Cognitive defects that preclude answering questionnaires or following assessment directions * Other unstable chronic diseases * Unstable medical conditions * Use of narcotics * Severe depression or anxiety (untreated / unstable) * Limited English proficiency * Investigator discretion that participant would not be suitable to participate * A phone older than 5 years old or unable to support EMA software HEALTHY CONTROLS Inclusion Criteria: * Apparently healthy with no known chronic illnesses Exclusion Criteria: * Pregnant or breastfeeding * History of POTS or orthostatic symptoms, migraines, fibromyalgia, chronic fatigue, PTSD. Functional gastrointestinal disorders, fainting, dysmenorrhea, or other chronic pain syndrome, inpatient psychiatric admissions, substance use disorder, trauma such as a motor vehicle accident, surgery, or other significant physical or emotional trauma in the last 5 years * Cognitive defects that preclude answering questionnaires or following assessment directions * Other chronic unstable diseases * Unstable medical conditions * Use of narcotics * Severe depression or anxiety (untreated / unstable) * Limited English proficiency * Investigator discretion that participant would not be suitable to participate * A phone older than 5 years old or unable to support EMA software