There was one time I went nearly 2 weeks without weed and when I got home I decided of course to break out the bong, I took a huuuuuge hit and vomited on myself. That's the only time I've puked or seen anybody puke while smoking.

I'm guessing your friend just has a virus or something (is that why he skipped school?) so you should probably not be toking on the same joint/bong as him unless you want it too.