I had to learn this the hard way:
when you take a vitamin with b6, make sure that you don't take anything else that could have b6 (enery shots in smoothies, red bull, other energy drinks, etc.). I took my multi-vitamin in the morning (i usually take it at night) and during the day I got an "energy boost" in a smoothie that I had, and I thought I was going to have a heart attack! My heart was going 100 mph. I thought I was having a blood clot or something. I finally came down though, I had to splash my face with some cool water.
But yeah, too much can be bad, it needs to be a good balance of b6.