Depends... If there's a solid barrier of some sort, it's fine. But a glass window, or one of those glass floors that allow you to see right down to the ground far beneath you... Or no barrier... Stuff that, that's just uncomfortable. I don't panic, or scream like there's a crazed murderer on the loose 5 meters in front of me. But I'm still worried and uncomfortable. I just move on and pull a really awkward facial expression like most do when they're in that situation. So I don't know if I would call it a fear, no. I just call it having a sense of what is secure and safe and what isn't.