3d view

So, recently i've decided to increase my model render distance. However, after doing so, hammer started freezing for a few seconds when selecting objects in 3d view. The more entities/brushes where on screen, the longer was the lag. The issue persisted even after returning the model render...

For some reason when I am in 3D view and I try to look up, it forces me to look back down with a jittering motion as if I had locked my mouse to one angle. What is weird is that when I look down, left or right, it is normal. What do I do?