Having same issue.
What I usually do is either close the lid, wait for the sleep LED on the side to start blinking 5-10 seconds later, then open the lid again. Or press power button and wait for the LED on it to start blinking, then press it again to wake up the machine.
Seems this happens when there is a switch in power mode (and probably switch between the 2 VGA cards in the laptop), as the same happens on an HP which also has 2 VGAs of the same type.