Replying to Sleep question

So I was cleaning my room, listening to music in full screen cover flow...(not front row).  When I was done, I simply closed my MBP and went to my soccer game. I got back and tried to open it and it wouldn't come out of sleep mode. I pressed space bar, escape, random buttons, tapped the trackpad blah blah blah but it just stayed black.  I eventually had to hold the power button to get it off.
Anyone had problems like this? Is there a magic way to make sure it gets out of sleep mode?