Q: Screen stays off after unplugged from monitor

I have a MacBook Pro Retina 13 I primarily use it at my desk with the lid closed, connected to power and two external monitors (one HDMI one Thunderbolt). When I disconnect the monitors & power (without opening the lid) and then try to open the lid to use it seems not to wake up.

The lights-behind the keyboard are not on, the apple-symbol on the lid is not lit and the screen does not power on. I've tried pushing the power button, nothing. I've tried increasing brightness incase it somehow thinks that I had decreased it. No dice. The only solution seems to be a hard-boot (hold down power button for a while until I get an apple-symbol on the screen). It seems to happen intermittently I'm not sure what the cause is! It's definitely not a battery because it's fully charged and after the hard-boot it operates fine.