When you want to share what was a UDIN moment for you, you can do so in this thread.
Although dramatic, there are "small UDINs" and "big UDINs".

I shared one of mine in a previous session: I suddenly realized at the airport that my passport was missing in my pocket! 
One moment I felt completely stunned, then the sympathetic nerves set in and made me search feverish, run through the aisles, focus my eyes on the floor and almost bump into people. The feeling was a "brain stem imparative: I MUST GET IT BACK!!!" and it suppressed a hundred thoughts what would happen if I didn't!
I had the good luck to really find it on the stairs, I shook with energy release, and recovered slowly on the flight. 
I have a certain affinity to losing things and a typical panicky emotional response when I lost someone or something out of sight.
I know I lost a key as a kid which also felt that traumatic, and I even track it back to my after-birth experience of being separated from my mother and twin sister and through that having lost the ability in my left eye muscles to look to the left...