How do I stop continuosly rereading sentences without understanding them?

I’ve been studying pretty much at all waking hours for the whole week. But I’m having this problem where while reading a lecture, I keep re-reading sentences several times without actually understanding/registering what it is saying. It doesn’t have to be a hard sentence or even anything complicated. It could be something as simple as “Voluntary contractions reflect a conscious decision to increase motor unit activity while reflexes reflect non-conscious drive” and I’ll still do the same thing.

Eventually I get frustrated enough to pay attention and understand what it is saying. But I don’t want to have to re-read in the first place. Does that make sense?

Any suggestions? I know it’s probably just because I’ve been studying so much, but it’s annoying and a waste of time. And I’m not even tired right now. Please make it stop!