Oh! I totally know what you are talking about!!!

I job-shadowed a vet in high school, and didn't realize that the smell of the chemicals of some procedure they were doing really irritated me... (or something, I know I'm not afraid of blood or surgery - I also have seen human procedures done in person too and never had any problems). I don't remember a whole lot, but I remember feeling really odd, and suddenly was like, I NEED TO GO OUTSIDE (I am terrified of getting sick inside, I'd rather be outdoors). I remember running to the doors and then I woke up in a chair and they were shoving food in my face.

I don't know if it will help any, but next time try to look away from the needle and/or blood. I remember feeling light-headed once when I was watching the nurse get ready, I'm not sure if it was anxiety or what, but I've never had a problem since.