Turn Monitor Back On after xrandr
Solution 1:
xrandr --output LVDS1 --auto
did it
Solution 2:
When accidentally disabling the only attached display, trying to reenable it from another virtual console will yield in the following error message:
xrandr: Configure crtc 0 failed
Please make sure the actual virtual console where X Windows is running is active, when xrandr is actuating the configuration. Typing the following in the first virtual console rescued me:
sudo chvt 7; sleep 3; xrandr --display :0.0 --auto