Well, I don't know much about B12, but B6 will greatly increase the vividity of your dreams. ~1-2 g (grams, not mg) should be safe, but don't use it every night for the best results. Also, never take more than 4g at once. It shouldn't hurt you, but taking 4g or more a night for a month can cause nerve damage. Like I said earlier, stick with 1-2g and you'll be safe.