Comment 5 for bug 1062166

I'm not certain which one thing fixed it, but here's what I did:

Open dconf editor from the Dash
Click on the Find, and type Power.
Here's what I've got set:
idle-brightness = 0
idle-dim-time = 0
sleep-display-ac = 0
sleep-display-battery = 0
sleep-inactive-ac-timeout = 0
sleep-inactive-battery-timeout = 0

Try setting those and see if it helps you. Again, not exactly sure which one thing fixes it - haven't taken the time to check. And ultimately, one shouldn't have to do this in the first place.