ALL of my video disappeared!!!

I don' t understand how, but this is the second time that this has happened. I went to save the video and accidently hit some key other than "s", and BAM!!!!!, ALL of my project is gone!! The project file size is there in the browser, but where is all of the work that I've been doing for the past three days?? What's worse is that I can't find the previous saves in the "auto-save" folder. What did I do wrong and how can I avoid making this terrible mistake again? Thanks