I've passed out three times in my life, and I think they were all due to emet/anxiety. But I actually have a heart condition too, so maybe that contributed.
The first time was the first month of school, and it was after the summer that I got a bad sv* (my first in 12 years) which sort of sparked my major emet. I had a really long day ahead and I was so nervous that I would feel sick and not have any anti-n* with me, since I had just run out. I worked myself up so much that I passed out while I was getting ready for school.
The next time was this year. I was getting ready for school, and it was going to be a really busy and long day too. I started feeling anxious about the day, and because I had a touch of d* brought on by my anxiety, I was freaking out that I might have a sv*. I got so nervous that I passed out and fell backwards into the slippery bathtub. I don't remember before or immediately after I fell, but I remember jumping up and running to my room before anyone would realize what happened. I got to my room just in time before I blacked out again.

Good times.