Diagnosis: POTS with associated low cardiac output, low systemic vascular resistance, excessive venous pooling, reduced blood flow to brain, impaired cognition, vagal dysfunction and moderate sympathetic failure. Likely Mast Cell Disorder. ME-CFS.  Peripheral paresthesia (possible sudomotor small fiber neuropathy.) Autoimmune response to vaccination.  Was completely healthy prior to vaccination  Onset of symptoms:  Approximately April 13-17 2021: HSV1 blister (unusual for patient, ongoing through Jan, 2022. Additional 6-7 outbreaks )  End of May 2021: Polymorphous light eruption rash (never had before)  Early June 2021: onset of debilitating fatigue and brain fog, episodes of near syncope, heat intolerance (never had before, ongoing)  August 10, 2021: onset of urgent diarrhea (lasts 6 weeks)  August 20, 2021: onset of peripheral paresthesia (never had before, starts in feet and lower legs, quickly spreads to upper legs, hands and full arms, accompanied by internal vibrations. Ongoing with flares.) Initial work-up at primary care negative.  September 2021- mid October 2021: weakness in legs, cramping, difficulty walking (ongoing with flares) Nothing found in initial neuro exam. MRI of brain and spine negative. Found positive IgG antibody to Ehrlichia. Treated presumptively with 7 days of doxycycline late September. Some improvement of symptoms in early October, now believed to be due to cooling of weather.  Mid to late October, 2021: Symptoms return. Treated with second course of doxycycline. Does not improve. Post-treatment IgG reveals no increase in antibodies. Second neuro exam. Orders additional labs including paraneoplastic panel. All negative.  Late October-November, 2021:  vertigo, dizziness, neck stiffness, heart palpitations, lightheadedness, constipation, vascular throbbing, tinnitus (both pulsatile and tonal), constipation, venous pooling, vascular instability, shortness of breath on exertion, tachycardia, shortness of breath bending down, exercise intolerance (all never had before, all ongoing) Could not complete EMG as it was too painful. Initial Rheumatological work-up. Notes reddening of feet. Orders Avise antibody panel. Negative, but for positive ANA 1:160. Audiological exam negative.   Late November -early December, 2021 Given course of oral prednisone. Experiences remission/improvement of many symptoms. Cardio workup. Holter monitor, echocardiogram, EKG all negative. Work-up by Infectious Diseases, all negative but for elevated CRP, EBV AB which are inconclusive.   December 2021: Purchases at home blood pressure cuff, reports heart rate elevations of over 30 bpm at home ?poor man's tilt. Confirmed by orthostatic bp in physician?s office. Autonomic testing is ordered. EMG and nerve biopsy completed. Negative.   Late December 2021 through January 2022: Experiences flare, possible reaction to contrast agent for MRA which was negative. Tinnitus becomes unbearably loud. Peripheral paresthesia returns. Experiences new allergies, skin rashes, certain foods, pain in hips, pain around rib cage, abdominal pain. Begins work-up for MCAS. Second course of oral prednisone improves symptoms as does initiation of H1 and H2 blockers.  Mid Feb- late March 2022: Immunology diagnoses likely Mast Cell Disorder continues H1 and H2 blockers. Begins PT for presumptive POTS, autonomic dysfunction. Improvement of many symptoms. Undergoes extensive autonomic testing. POTS diagnosis is positive with tilt table test. ?POTS with associated low cardiac output, low systemic vascular resistance, excessive venous pooling.? Testing also indicates reduced blood flow to brain, possible cognitive impairment, possible autonomic neuropathy, vagal dysfunction, and moderate sympathetic failure.  Late March 2022- present (4/15/2022) Flare of symptoms after travel. Increased peripheral paresthesia which spreads to trunk (upper back and buttocks), internal vibrations, pain in hips, worsening venous pooling, orthostatic intolerance, very elevated heart rate upon standing, extreme fatigue and brain frog, loudening tinnitus, throbbing vasculature, pulsatile tinnitus with postural shifts, heart palpitations, shortness of breath on exertion.  Started on course of prednisone 4/12/2022