What Leads To Sudden Vomiting?

I was a little concerned because out of nowhere I felt sick and had to puke, it looked like little pieces of tobacco but I only ate early in the morning and had coffee throughout the day. I felt the same way this morning out of nowhere but not enough to make me puke and only lasted for a few minutes then I was fine. Also it tastes like acid but I figured that's because I didn't have nothing in my stomach.