Being naked in front of brother/sister

When I was 18 and my sister was 21 I went to visit her in Germany where she lived. My sister hadn't seen me naked since I was about ten years old. When I was there I became quite ill and had to visit my sisters doctor. My sister had to come in with me as I spoke very little german. Almost immediately I had to strip to just my underwear to be examined by the female doctor. This was embarrassing as my sister was sitting only a few yards away. The doctor examined me but just as I thought it was over she suddenly pulled down my underpants. My sister could see everything and I could see that she was looking at my $%!@. As the doctor examined my $%!@ I also started to get an erection which my sister had a full view of. I ended up completely naked in front of my sister for about five minutes and it was the most embarrassing thing that has ever happened to me!