I'm sure by now you've probably found your answer, but wanted to mention this anyway. Niacin is an antagonist of Potassium. Taking Niacin might have caused pretty bad Potassium deficiency. Signs of Potassium deficiency are exactly what you describe - "chest tighness, neck pain, lost appetite. Massive heart awareness..." as well as kidney issues, poor circulation (feeling cold, cold extremeties), insomnia, irritability, anxiety. I cannot imagine taking 8 grams of Niacin without taking any K (Potassium)! And please, remember, we need Magnesium in order for Potassium to enter a living cell. Hope this helps.