This happened to me when I took a lot of vitamins and was hypersensitive to them. It started when I took a lot of the Bs and a bunch of other vitamins years ago. Each time I'd take them, my heart would race, chest would get tight, and I'd feel panic, and I had a spaced out lightheaded, almost a feeling like I was on something (but it was not pleasurable). I found when I stopped taking the vitamins it got better. For me it was a sign of overload of things that I cannot tolerate. It is possible you are just intolerant of vitamins in general or of the Bs. A lot of people have a hard time with the Bs I know.