Stop passing out in hospitals?

Blood and needles have never bothered me, but a few months ago I was in a dialysis center and I think it was the overwhelming smell that made me pass out. Again, a month ago I was in a hospital watching someone get blood drawn and I was paranoid that I would pass out from that previous experience. I started getting light headed but I was fine. Is there a way I can overcome this? I think it has something to do with the smell of hospitals and the fear that I will pass out...