Why did i almost faint when using a tampon?

It's more likely that you were about to faint and feeling nauseous because of the blood (and iron) loss than from the use of tampons. In my experience, when I first started using tampons, I was tense as well. But it didn't make me feel faint. If you actually faint and/or vomit, you might want to ask your doctor about why you may be feeling this way when you're using tampons.