Why is it that when I drink vitamins I get heart palpitations?

Energy drinks. Many vitamin drinks have caffeine or similar substances in them. Kola nut extract has caffeine. They may also contain ephedra or similar substances. Some vitamins can cause issues at high levels, take a look at the vitamin content of what you are drinking and make sure you are not taking in enormous doses. Also, see what herbal additives are in there.
Unsure. Are the vitamins you're drinking part of an energy drink? Are you drinking, or do the vitamins contain caffeine?