If your mac laptop screen goes black for no reason after a sleep, it's called the 'black screen of death':
MacBook Pro Video Update 1.0 (Snow Leopard)
This update addresses an issue where MacBook Pro (15-inch Mid 2010) computers may intermittently freeze or stop displaying video. For detailed information about this update, please visit: http://support.apple.com/kb/TS4088. The update is for Snow Leopard.
Some people claim it is fixable. Apparently if you boot with the shift key down, it turns the screen back on. I tried it and it seemed to work. The reason I was forced to investigate was MY laptop started doing this. So much for apple quality. At any rate, there was another webpage that says that after you've booted, delete /var/vm/* - ie open terminal, type
sudo rm /var/vm/*