This happened to me once when I was in Germany and was with a girlfriend who had a sportscar -she was doing around 140 km, and I was so petrified I was frozen and sitting right down in the street.
I felt she knew what she was doing, so when I could move my mouth I asked her would she not getting booked for speeding and she said no, she was OK -from memory there was no speed limit where we were.
Suddenly we hit West Germany -or came close to it and the freeways turned into cobblestone roads, and still she sped and by then I had my eyes shut and was prayinbg!!!
I was sure it was my last minutes on earth.....
Nowadays in Australia, I think I would say that could she please slow down as I am nervous.