I've had something a little similar just recently, but mainly towards the end of my long runs. After about 8 miles I've started to feel sick for some reason. It may have been from eating late at night as I was out running in the morning, although I wasn't actually sick. I did also think it may have been the warm weather. In fact, on Saturday I ran a 5k trial and I was virtually on the verge of throwing up as soon as I crossed the line. Perhaps there is a link with exhaustion there somewhere.
When the kiwi threw up after his effort in one of the rowing events in the Olympics, it was suggested that it was down to his lack of fitness in relation to the effort that he was attempting to exert. He was over working his body.
I've never thrown up from running. Felt slightly nauseous the last couple of miles on my Sunday run, but I was hung over. It's really not normal to be physically sick, even if you have been pushing hard.
Come to think of it, the last time I physically threw up was back in 1996. I remember it not being pleasant.