files disappearing from SD card

I took a few dozen shots with my 60D, looked at a few frames on the camera's screen and then set the camera down. Later, when I inserted the SanDisk Extreme 16GB card into my computer, not one of the files was there. Earlier files were still on the card, but the last few dozen had vanished.
Can anyone suggest what stupid thing I could have done? Nothing like this has ever happened to me before, and I certainly don't want it to happen again.
Thanks.

Did you look in every subfolder? My cameras are set to begin a new folder when a certain file number is reached.

Thanks. Yes, unfortunately, I did look in subfolders.

Try putting the card back in the camera and see if the new pics can still be seen on the camera's LCD.

No, I can't see them on the camera although I could initially which makes me think they were on the card at one point.

Do a test to see if your card is not counterfeit. I recommend you download and test your card using the utility on this page

http://sosfakeflash.wo​rdpress.com …g-usb-counterfeit-drives/

The way card memory works is that sometimes on a bad batch a 32gb card will not be discarded but will be remapped as a 16gb and sold cheap to someone. Unfortunately that someone can be unscrupulous and remap it again at 32gb. The header on the card will s how 32gb and it will format normally and will seem fine until you save something on the corrupt part of the memory. It is quite surprising how many counterfeit cards are out there and sometimes even from reputable sellers that also got duped. It is a good idea to test every card you have to make sure it is good ... nothing worse than taking some memorable shots only to find out they are not on your card when you get home! All counterfeit cards I ended up with were bought from Ebay, some of those sellers had stellar reputations. My recommendation is to pay more and buy from one of the good reputable shops (Adorama etc...). If the price seems too good to pass up then chances are it is fake ... or at least don't consider you got a good deal until you run the card through the utility.

Thank-you for the information about counterfeit cards.
What baffles me is that I played back some of the images 5 minutes after I had taken them. Now, only that batch of images is gone. The whole batch. It makes sense to think I'm missing part of the story, but the card did not leave the camera between when I took the pictures and when I inserted it into my computer. I keep hoping for an epiphany, but nothing's coming.

^ could it be a utility on the post processing software wipe it each time?
EI "format images after import" box is checked?
I know my Iphone ALWAYS asks if I want to Delete imported photos and I keep says NO...

No reason why other than the above or possibly a bad sector, but just use Photorec to recover the images. If it's a bad sector you might be out of luck, but you can try.

http://www.cgsecurity.​org/wiki/PhotoRec