Recently, I have trouble concentrating. I notice that I cann't focus on the documents when I check them. I had such a situation in college, I couldn't check my homework, because I couldn't focus. Do you have such a problem? I found this article https://booksrun.com/blog/feeling-sleepy-when-revising/ there have a lot of tips on how to deal with it. Do you think they are effective? What advice would you recommend? I don't like this condition, but I try to cope with it.