Niaspan ER and sheer panic

My GP, (doctor) prescribed Niaspan Prolonged Release Nicotinic acid (Ph Eur) 8 days ago to lower bad cholesterol. It came in a starter pack 7x375mg - 7x500mg-7x750mg for three weeks to run consecutively, which I take in conjunction with Zimverstatin 40mg nightly. First 7 nights, no problem, last night started the second week dosage...and after taking the first 500mg tab, I got busy on my com for a while...as you do...then Bang! I began to burn up inside, sweat leapt out of me like a garden sprinkler, I went weak, nauseous, ran to the loo (Toilet) ran around the house in sheer panic as my heart raced so fast, it felt like one continuous beat, then I nearly collapsed. On passing the bathroom mirror I saw my palour had gone to a waxy-grey, then I instinctively took two 75mg aspirin, and in the end collapsed on the bed. I woke up about 20 minutes later and realized I was not in heaven as my room was still as untidy as it normally was...never mind. I am waiting for a call-bcak from my GP...there are things I need to know as I suffer with angina....thanks for reading this.