I had an interesting experience with a Niacin Flush.
I had been taking Niacin for some time without experiencing any "flushing". In was in a multivitamin and I hadn't paid much attention to it.
I started practicing Yoga Nidra (Conscious Deep Sleep) about a week ago. I was a little bit surprised that I experienced a Nicain flush yesterday and today. I had to check the label to see that I was taking Nicain and not experiencing something else.