When it happens, my laptop screen goes black for a few seconds, except for the taskbar and toast notification. I also have an external monitor that doesn't seem affected at all.
I can reproduce the error pretty consistently if I rapidly switch a Flash video back and forth between full-screen and embedded, but that's not the only time I've seen the problem.
As far as I can tell, everything continues running. Even the full-screen video continues running after the screen isn't black any more.