Ouch, I thought all Mac Users know this, that's why I suggested SMC reset, good it is solved.
Macs do have sleeping problems once in a while, I have a new Mac Mini and it failed wake from sleep 3 times in a week, I set the sleep timer to never and it is solved for now, put to sleep manually.
There seems to be a bug in 10.8.2 and lots of people have this problem.
How can we know this, if you do not tell us the model# or the generation of the MBP!?
If it is a model from 2007, 2008 or 2009, then it is possible, that your model has a defective NVIDIA GPU. I had a defective GPU in my Mid-2009 17" MBP.
In that case, a professional repair shop can help.