Computer being weird.

I usually put my computer to sleep when I go to work. When I came home today I found that it was awake (no idea why) and all active programs were opened up (instead of being hidden). My bluetooth mouse and keyboard would not connect to the computer and the programs were unresponsive. I decided to reboot and when I finally got back at the login screen, in big red letters it said "Safe Boot". What is this all about? I did not login here and decided to reboot again and everything was back to normal. Any idea what could have happened?

Thanks!