Back when I first started smoking, I was with some chicks and another guy and we smoked a bowl and then some salvia. Once the salvia was finished, the guy we were with started having some sort of seizure. Shit scared me sober. We were dumb and didn't call for help cause we were young and stupid, however it only lasted a few minutes. He told us he had drank WAY too much caffeine and in combination with the weed and salvia made him seize. Apparently this happens a lot to him, even without the salvia, and he just didn't feel the need to tell us before he scared us all.