When in fullscreen watching videos, the screen flickers black and purple

For a while now, whenever I watch any video on fullscreen the screen will flicker black lines or just fade to black completely for a second. It used to be tolerable, but I've started to notice that it's gotten more frequent. Purple lines have also started to show up when I go into fullscreen; one time, it recently just froze my entire computer and purple lines were just filling the screen while I was watching Twitch on fullscreen. I had to to a restart because of it.