I don't even know what it is. I literally didn't even know it was that kind of bridge until I got home and googled it. For me, it was a physical sensation. I couldn't even see the water, how high I was, or anything around me other than the road. But, I can honestly say I cross the 288 concrete bridge near Goochland and Powhatan line and don't feel any sensation. But, this bridge, my body knew something was different about it even if all I saw was the road. I am wondering, if for me, it is more of an altitude sickness. I know I get the same feeling with underwater tunnels though.