I guess it is because the screen is changing contents more frequently than you liked. Also because the YouTube video has terrible frame rate on the webpage. Low FPS tends to cause motion sickness, that's why my CS:S is minimum at 75fps. Anyway, mine Win8 is not as busy has that. I shrinked the tiles, so, it fits more apps in the screen. And I have ModernMix to pin my mail app. I don't care much about the live feed. Just showing me new message count and I will launch the app, which basically works after I shrink the tile.