Hi Bachus,
You've got to try and remember to back your stuff up, especially if you're doing something major. I do a "save all" to my hard drive , plus both my USB sticks.
If I'm only working on user styles, I just do a save of the styles.
But end of day, if I have made changes, I do a Save All.

If you do goof up and press a wrong button at the wrong time, from a save all, you can load individual items back in or you can load all your user stuff back in.

Also do Back Up. Different to Save All. Worth studying manual on differences om what gets saved.