I'm sorry that your videos went missing. I have a fav dvd that I do continuously. I have 7 in all (some of them i will have to loose more weight before i can jump around like that), but i keep them next to the dvd player so they don't get lost.
I'm a packrat, so I know how easy it is to lose things. Try clutter busting while walking around the house. You probably had the dvd in your hand and went into the bathroom put a new roll of TP in there and randomly put it on a shelf on the way there. Trust me, things get everywhere...
If you do buy a new one, donate the old one (whenever you find it) so that you know that someone, somewhere, who will need it will be able to use it. And you are helping your fellow (wo)man.
~Tanya