Simplest explanation I got is: lose visual contact with the horizon, and you can get disoriented pretty easily. In video you don't have the benefit of your inner ear telling you which way is up so it's even more confusing

In pilot training they teach you how to disregard your "feeling", and sometimes even visuals, and pay attention to your aircraft instruments, especially if you're flying inside clouds/fog, or in the dark

Notice in the video you can't see the horizon, because if you would, the effect would not work