Weird screen flickering only while watching YouTube in fullscreen

I was very terrified that either my GPU or my laptop's screen was dying but it wasn't happening anywhere else , only while watching yt in fullscreen and then I remembered that this has happened once or twice before too with one or two specific videos. So please help me identify the issue, also if the information helps I'd like to tell that my GPU was showing to be on in the tray but my laptop was in optimus mode.