This is an original 15" rMBP from July 2012. Running Mavericks. I just close the lid to put it to sleep when not in use as I always have done, but in the last couple of days it has not woken when I've opened the lid again. Pressing a key or clicking the trackpad doesn't wake it either. The only way I've found to bring it back to life is to hold the power button down for 20-30 seconds, at which point it actually starts from cold (as though it shutdown when I closed the lid). It doesn't happen every time and I've powered it down and back up after it happened the first time just to make sure everything was reset, but the problem persists. Has anyone else seen this? Any ideas? Thankfully I've got AppleCare should it die, but I'd rather it didn't. EDIT: Oh, and before anyone asks, yes, it has plenty of charge left in the battery (>50%) when this happens!