pigboat, yes I get it sometimes to a lesser degree if flying low over mountains in a helicopter. Happened last week between Swansea and Cardiff. The valleys heading north from Cardiff are very steepsided, and when I went from being less then 500 feet above the ground (avoiding low cloud, and no people etc so not breaking any rules) to being about 1500 ft agl - ooooo...felt very strange, didn't like it at all. It was, as you say, the ground falling away that was the problem, as vertical take-offs in a helicopter are lots of fun and don't bother me. Very odd.
Whirly
------------------
To fly is human, to hover, divine.