Is it normal that i sometime pass out from this?

Sometimes, if I'm grossed out by something or think about slowly dying somehow, I'll pass out or more often, just have the beginning stages of passing out. When I pass out, my ears ring, then I see colors, sometimes feel nauseated, then I pass out. When I was ten years old, my mom showed me a pamphlet of farm animals being mistreated and my ears rang and I saw colors. I didn't know what this meant until I was twelve years old. When I was twelve, I had to do a worksheet on a Current Science magazine. One of the sections was about bedbugs. The week before this, I had bedbugs and had more bugbites than I ever had from the bedbugs. The day before this, I got two shots at the doctor. I thought about dying from bedbug bites and shots. Then, I passed out. Often I feel like passing out just from hearing the word blood. Is this normal? I've never thrown up from this kind of stuff, just passed out. I'm eighteen years old and I still feel like I'm going to pass out from this kind of thing.