This has been happening for several months and I had MacBook checked out at Genius Bar - no problems found. It goes to sleep while I am reading email or an article and won't wake up for 20-30 seconds. Nothing on screen except arrow that doesn't respond to keyboard or touchpad. Very annoying for impatient users. Anyone else having this problem? I am up to date on OSX 10.9.4. It eventually wakes up without a restart.