My lappy has 16 gigs of memory (yay me), and when the machine goes in to a deep sleep / hibernation, it effectively powers down. Upon wake, memory has to be read back in from disk, which can take a noticeable amount of time. While that's happening, the screen is blank, and the computer is inert like it has totally died.
Once you've totally finished panicking and starting your recovery plan ("dammit now I'll lose a day's work getting this to a genius and re-cloning my repos to another machine") the memory has finished swapping in and the machine wakes. "Hi! Now that you're completely carbonated, let's get back to work!"
Unsurprisingly, major OS updates seem to reset this value. (Firmware updates may do it too.)
(This may be incomplete - I have a couple of days still to make sure it totally works)
Turn off hibernation with:# sudo pmset -a standby 0 # sudo pmset -a hibernatemode 0