Lost spreadsheets

In the last month, I have had several Numbers spreadsheets just disappear. Tried finding them using the search feature. Tried deleting and reinstalling Numbers. Still nothing.

On top of that, several old spreadsheets that had been trashed have suddenly reappeared.

Using a MacBook (OS X 10.9.2) and Numbers 3.2.

(I have not backed up any data on this computer because, so far, I haven't saved anything on it that is critical. The lost spreadsheet can be recreated fairly easily and, before I do anything else I promise I'm going to learn how to do a back up.)

So my question is this: Is there any way to retrieve the lost spreadsheets? What happened to them? Is this a problem with the Numbers updates?

Any help is greatly appreciated!