In previous versions of minecraft, the faster you moved your mouse, the more your head would turn. For example, if your sensitivity was on 70%, and you slowly moved your mouse 6 inches in one direction your head would turn less than 180 degrees. If you moved it extremely quickly 6 inches in one direction your head would turn more than 360 degrees. 

In 1.13, the degree of head movement stays the same whether you move your mouse quickly or slowly which feels unnatural. When running around in a world, if I want to turn my head around on 70 or so sensitivity it takes two strokes of my mouse across my track pad. The obvious solution would be to increase the sensitivity, which then makes interacting with furnaces or chests next to each other difficult from the player head turning quickly.

I think that whatever was changed with the mouse sensitivity should be reverted because it is unnatural. In windows 10 the faster you move your mouse, the farther the pointer goes. Constantly switching between natural mouse physics and the new mouse physics in minecraft 1.13 makes getting used to these controls very difficult. I'm not sure if this will be considered a bug, but if it is an intentional change I ask the developers to revert it, or add a button for players to choose between new and old mouse physics. I know this is a long post, but thank you for reading.