Yikes.
I am presuming this is the first time you've had this problem, and that you've had the machine in sleep mode in the past with zero problems.
Does rebooting resolve the problem (until you put it into sleep mode again, I presume)? Is this problem repeatable and consistent, or is it random?
Did a firmware (EFI) update get installed automatically?
Or system updates in general?
What version is OS X (10._._) - if bought in Sept of this year, I'm thinking 10.8.0 or 10.8.1 would be stock, and possibly upgraded since with 10.8.2?
It's also possible a patch could introduce bugs as well, but not likely - unless others chime in with the same experience... Apple's benefit is controlling hardware options, to keep this sort of problem to a minimum...
If it's a new problem and you know it worked before, and nobody else has the problem, and your system is fully up to date and patched, get it in for a warranty repair. Stat.
