Is this a normal situation?

This question may seem a bit strange to those reading it. This is something that has been in the back of my mind since I was in middle school, I have never shared this with anybody, so please no one slander me for anything that might appear weird in this question. In my middle school years and early high school years I was always very shy around girls and could never get a girlfriend. I would have fantasies about being with a girl, but for some reason I recieved pleasure in fantasizing that my girlfriend was a 50 foot tall giant. Now that I have grown older and am in college and have had a girlfriend before I no longer have these fantasies, but I still fear that the kind of fantasies I had were sinful lustings. The fact that the fantasy is not somthing that most people think about disturbs me greatly, and as a practicing christian it disturbs me that I do not have the courage to talk to anyone about these past episodes. Any help from anyone if this is normal, just a result of my difficulty in talking to girls making them seem like some giagantic thing that was always impossible for me to reach? Would this fantasy be similiar to a ographic fantasy? (Somthing that I have never had)