Mars Worm in the chatroom is having issues with his hard drive unmounting in his Mac Mini when it goes to sleep. Leo says that computers going to sleep has always been a pain, going back to the early days. Hibernation is even worse.
Mark has been having similar issues with his computer crashing when it goes into hybrid sleep or hibernation. Leo says that hibernation has never really worked the way it's supposed to. It's just best to turn it off. Hibernation saves out the RAM and then when you turn it back on, it has to load it and often it'll crash. So just disable that option.