Even worse at night

It's weird...it's really just this one specific bridge.  It's high in the middle --or looks that way anyway-- and going up it at night I have the sensation that I'm about to slide backwards down the slope of the bridge.  The fact that I'm aware that is completely impossible doesn't seem to matter to me.  But it gives me the willies. And I have you to blame, is that it, Mom?  I never used to get this feeling. Weird.