I closed the lid on my MacBook and came back to it around five minutes later. Nothing happened when I opened it so I held the power button and switched it back on again. It was very sluggish to start up, holding on the blue screen for a few minutes before allowing the user account login screen to come on. When it finally let me login I checking the Console which has 'display: Not Usable' noted at the time it happened. Should I be worried about this or was it just a freak incident? Thank you for any responses.