What kind of display issue is this and how to fix it?

I had an issue with the vents of my MacBook. I’ve opened it and used a vacuum cleaner to get rid of the dirt and dust inside the coooling system. After that my vents worked like a charm again - but I seem to have caused an issue with the LCD screen.

When I hold the MacBook with both hands and twist the bottom, the LCD backlight at the bottom of the screen bleeds in two variations and the whole screen is in general switching between bright and rather dim. See pictures below (only showing a white background, the difference between a bright and dark screen can't be seen in a photo but is very noticeable in real life):

https://postimg.org/image/oe651h4rx/

https://postimg.org/image/7ex6m7tkd/