What are the effects of staring at a computer screen 15 hours a day?

Fatigue : When you look at anything to focus, a lot of activity goes on in our brain as well as other parts such as eye muscles. We need to take break and give time for our systems to reset. If we cannot afford to do that we will get headache and other signs of fatigue; our productivity will go down; we just get the feeling of doing our best: however, without the best result.