GPU usage spikes when looking downward, it is also possible to achieve this effect by going below the bedrock and looking up. It seems to happen when the player is looking at blocks close up, as it can be reproduced by digging a deep hole and looking horizontally.

*Steps to reproduce*

• Create a new superflat world, mine was the default redstone ready
• Make sure you stand on the ground
• Look down

example: https://gyazo.com/3cb3d594ac371affb9fb69ca8ed4f9dc