Insanely slow to find files

When I am in a program and I try to open a file, when I click a folder to view it's contents I currently get the little "loading" wheel in the bottom left of the "open" window for a good 10-15 seconds before files start showing up. It's really worrying me as I think my hard drive could go kabuggerboom at any moment.

I have noticed it does this in any program and with any folder, regardless of how much/little is in the folder. It's only done this the last few days - anyone else had this problem? I will take it into an Apple store next time I am near a city with one in, but at the moment I am scared of losing all my data but at the same time can't live without my MBA (work).

Somebody please shed light on this issue and tell me everything's going to be ok?