I get this way but I also have diagnosed OCD. I'm always counting page numbers and wondering when I'll finish or if I'll ever finish. I have to remind myself to take a deep breath and pause and visualize/enjoy the page I'm reading

You may also need something structured like a timer set when you read. And telling yourself, I will only read until the timer is up. Then I will put it down no matter what page I'm on. May help you enjoy it in smaller chunks?