OS Reset Itself

Quick question, I was scanning a document last night and my Macbook froze. I tried force quiting the application, but it didn't work. To get things moving again I restarted the computer, which it had no problem doing, but when it came back on the OS had been completely reset (wallpaper gone, dock changed back to default, trackpad not clicking, etc.). Luckily, I didn't loose any data. Any idea what happened and how to prevent it from happening again?