My MacBook Air randomly turns off its display after some time while actively using it.

I'm not totally sure why this happens. I'm not idle and actively using it when suddenly, the screen is turned off and even when I try to turn it on again by pressing buttons on the keyboard, it won't activate. However, when I move the display down then lift it up again (closing-opening action), the screen turns on. I recently updated to the GM candidate of macOS Sierra by the way.

I'm using also a:

MacBook Air (11-inch, Mid 2013)

1.3 GHz Intel Core i5

120GB version.