May also be performed unintentionally by males while shaving. The pressure of the razor blade over the carotid sinus under certain circumstances can trigger the same response, sometimes resulting in a faint.
I know this because it happened to me. One second I was shaving in the mirror, the next I was lying on the floor, blinking and wondering what had just happened. I was terrified I had a brain tumor, and went straight to the doctor. He calmly explained to me what I had experienced. No harm done. Apparently what concerns doctors most about the phenomenon is that people often suffer concussions when they fall.
j3z_ mentions standing suddenly, and that is exactly what this was like. Your vision just goes black. I have only felt like I was going to pass out when standing up, however. This time, I really did lose consciousness. Interesting analogy, though.