I used to work in a big metal building with no windows. The only sunlight came from the big cooling vents high up near the ceiling. I can relate, it sucks the life out of you. I found it better to take a few minutes to walk around, even if it's just (in my case) the department where I worked or (in your case I guess) walk around your floor or take the stairs to another floor and walk around there. It will at least trick your brain into thinking you're exploring something new.
BTW, I went back to school when I was 28 and changed careers. I fled the building with no windows and never looked back. I took a pay cut because I completely changed careers, but I've never been happier. There is no monetary value on that.
If I just said LOL, I lied. Do or do not. There is no try.