I have a little idea how other people read books, but I know for sure that it may often be stressful. For me, it definitely is because I read mostly in English, which is my second language. Other factors, such as the complexity of text and familiarity with a topic make it more painful as well.

It's not like I'm complaining. I'm just stating the obvious. Personally, I've been complicating things here myself as well. I used to read in strict time periods. That is, I would stop reading when a timer goes off.

I had applied the same method to many other things, like studying or exercising. It worked in some cases, so it was only natural that I would try to use it for everything.

In my opinion, the better way is to avoid ceasing reading abruptly and stop at logical pauses instead. That is, when the current (sub)chapter ends. Even if it's hard and takes some time.

Oh, and of course, it's important to read regularly because while the content of a book is fresh in one's memory, it's much easier to read it.