Sometimes the speed reading method helps when I'm not feeling engaged in the material. You don't have to read quickly. Just use the underlying format.
Before reading a chapter:
Read the test.
Read titles.
Read summaries.
Cover all highlighted elements before reading the chapter in a straight narrative fashion.
If you're still not engaged, take notes by hand, doodle in context, make a cheat sheet (that you won't use), or flash cards.
Always get up and move when you take a break. Exercise. Shower. Eat. Good luck.