The chief secretary of the Spanish Society of Allergy and Clinical Immunology based in Madrid answered my e-mail in which i told him the results the Niacin is having against POIS, saying that he does not think that POIS is an allergy related syndrome(Due to the effects niacin is having), but a Dysautonomic one. He did not elaborate the reason. Anyway, we will continue with the allergy hypothesis and i will make an allergy test(Skin-prick i suppose) to watch the results.
Dysautonomia (autonomic dysfunction) is a broad term that describes any disease or malfunction of the autonomic nervous system. This includes postural orthostatic tachycardia syndrome (POTS), inappropriate sinus tachycardia (IST), vasovagal syncope, mitral valve prolapse dysautonomia, pure autonomic failure, neurocardiogenic syncope (NCS), neurally mediated hypotension (NMH), autonomic instability and a number of lesser-known disorders such as cerebral salt-wasting syndrome. Dysautonomia is associated with Lyme disease, primary biliary cirrhosis, multiple system atrophy (Shy-Drager syndrome),[1] Ehlers-Danlos syndrome, and Marfan syndrome for reasons that are not fully understood. In a study on orthostatic intolerance and EDS it is suggested the occurrence of these syndromes together can be attributed to the abnormal connective tissue in dependent blood vessels of those with EDS, which permits veins to distend excessively in response to ordinary hydrostatic pressures. This in turn leads to increased venous pooling and its hemodynamic and symptomatic consequences.[2]
http://en.wikipedia.org/wiki/Dysautonomia