Obviously it shouldn't happen, but there is always a risk of failure on any storage device, one thing to be careful of is powering off or removing battery while the card is in use i.e being scanned, data accessed (such as playing music) or written to.
I'd advise plugging into a pc in mass storage mode, backing up everything to the pc and then formatting the card. If there are any lost files, try downloading 'Recuva' from Piriform to your pc. It's a free data recovery program, works also with external storage devices, I have used this on my own Galaxy S.
I would also keep a backup copy of memory card on PC, at least short term, if problem returns you might be looking at a faulty sd card.
Hope this helps