I love roller coasters, why am I scared of flat rides?

I know, for most people it's the other way around. And I don't get motion sickness. I will go on any roller coaster, but I have to really think before going on a flat ride. I went to Kings Dominion and rode the Intimidator 305, but then it was really embarassing because I wouldn't go on the Drop Tower, Berserker, or Crypt. I will say to my friends, "I will ride any roller coaster, it's the flat rides that I'm not so sure about." Then they will look at me like I'm crazy. So why am I like this and what do I do about it?