What Are The Side Effects Of Niaspan 1000 Mg?

I am a type 2 diabetic and my doctor put me on Niaspan to lower my triglyerides. I was taking one 500 mg. pill with no problem. He recently wanted me to take 1000 mg. I did for about 3 days and my blood sugar was 536 only one time. I have been vomiting on and off for 3 days. My sugar is now in the 150-200 range. Should I give up the Niaspan? I have also had dizziness, more when lying down. I appreciate your help.

Janet