Hi, welcome to the forum, symptoms are suggestive of drug allergy and are mediated by release of histamine
in the body. Your
body is known to hypersensitive to Niacin. Flushing, hypotension is known adverse effect of niacin in some individuals.
The spectrum of these reactions can vary widely; reactions may present as typical allergic symptoms (eg, itching, urticaria, rash, edema) after a single dose, or may manifest as severe idiosyncratic dermatologic reaction.