I just took the GRE in late August and scored 168V, 164Q, and 4.5 W, for what it’s worth. I think I stayed somewhat attentive and fresh for a few reasons.
First, I only took one simulated practice test, so I might’ve avoided overall burnout on the material. Second, I studied less than one hour per day during my study buildup, which decreased overall burnout, again. And third, I experimented with properly balancing my caffeine and water intake in the weeks prior so I could stay totally amped the entire exam while avoiding the need to run to the restroom. I had this approach down to a science.