Those of a nervous disposition look away now......

This is a true story.  It happened to me today and yet I still don't know quite how it happened.  Anyway, this morning I had to go to a meeting in another workplace.  You should know that my job requires me to wear a lanyard round my neck with my office swipe card, door key and ID photo hanging off the bottom of it.  Before I went into the meeting, I went to the loo to spend a penny. An hour later, I spent another penny before the long walk back to the car, along many a corridor and past many people, mostly male.  As I got into the car, something caught my eye on the end of the lanyard.  There, stuck firmly to the swipe card was a panty liner.  Not just any panty liner, but the very one that just over an hour previously had been stuck equally firmly (or so I thought) to my pants.  Now what I want to know is:

1. on which trip to the loo did the transfer take place and how?
2. did anyone notice but feel too embarrassed to tell me?