Optical illusion

Fellow vertigo sufferers will probably relate to this much easier than those who can look down from great heights without feeling the compulsion to just tip over the edge...

This was when Pete and I were driving up in Scotland, near Ben Nevis, the highest mountain. The road was extremely hilly, going up and down steeply. Every time the car reached the top of one of the humps, it was facing up at such a steep angle that I couldnt see the road ahead. I KNEW the road didnt end there. And, yet, every single time I had the completely irrational but completely convincing and deeply panicky feeling that we were at the top of a cliff and that's why I couldnt see the road ahead. I kept seeing mental images of Pete blithely driving our car onward and toppling it over the edge. I didnt tell him what I felt in case I came across as a total berk - but... brr... heights do my head in!