Joe Feise wrote:

His post shows
Organization: hispeed.ch, so if you are in Switzerland...

Bingo.

Over here, one of the few glider flights I had made me feel bad in the stomach,
which is rather unusual for me. But we were doing really tight turns, and I
probably looked too much at the ground.

Don't feel bad about it, you share this experience with a lot of first
timers and even with some power pilots. The movements when thermalling
can be really extreme (tight turns in rough air), but you get used to
it. That's one reason why some say that a first time glider ride should
just be a simple sledge ride with no thermalling. I don't agree, but I
am very careful and stop all thermalling immediately at the first signs
of uneasyness of the passenger. After all, a passenger ride should be
fun for the passenger.