Mac Crashes and Computer Reverts to Weeks-Old State

[degas]

Twice in the past two weeks, not even using my macbook pro, it was just on, and it crashed. When it automatically rebooted, the browsers opened up to pages that were opened days, if not weeks, before. That's not a big deal. But files which were on my system were now gone. Downloaded files, created files, everything. When I rebooted two or three times, everything returned. I'm at a loss. I'm running El Capitan, 10.11.2

Thanks!

 

[JohnDS]

Open Disk Utility and run First Aid.