What is the best possible reply for the "You are being lazy" statement?

I am doing a masters degree and I have exams soon. I am reading a 3000 pages course book. I am not taking any more courses or doing any other work while I'm studying. It's the hardest thing I've done ever. The truth is, studying so much is really exhausting. It's not possible to be studying so much for hours and still being excited or not tired. I am so tired now and I am chilling so my close friends get angry and start to say "you are being lazy" or "you are not studying at home". They just think that I am always being lazy and I am not studying at home because when I am studying, I don't go to the library. They say that if I was really studying, then I would say "oh, I am studying. You go to the park without me". I don't know, I am really tired and stressed and I think studying at home is boring as I am alone. And my friends are not studying and they think that I am not studying when I am chilling so they think that they should get angry with me. <br><br>What should I say to this? I am tired and I don't think studying 3000 pages is being lazy.