Given the small amount of blood depletion you describe, I think the posters here who mentioned vasovagal response are correct.

Remember too that different people will have different degrees of response to vasovagal stimulation. When we were practicing IV sticks in EMT class they had us pair up with a buddy and sit on either side of a small table. There was a pile of IV gear there and we took turns placing IV catheters. It didn't bother some folks at all, while others just about passed out. My partner was doing fine until the instructor came by and grabbed the catheter I had placed to see how well anchored it was. My buddy turned white and almost passed out...! <img src="/images/graemlins/shocked.gif" alt="" />

Here is a reasonably good overview of the vasovagal response.