I've had this problem ever since I could remember. I'm an entrepreneur, and my job consists on working on a computer for 8-10 hours a day. However, whenever I'm on the computer for more than 3 hours, I naturally get a headache. The best way I could describe this headache is like the feeling you get when your exam is tomorrow and you have 20 sets of slide to read for the first time. It seems like the only way I could get rid of this feeling is through walking and talking to other people (even reading a novel wouldn't help). But even after I've done walking/talking and got rid of the headache, it returns when I return back to reading/ the computer.
Sometimes it doesn't even have to be work - I could watch tv all day and sometimes get a similar feeling.
I've lost lots of productivity because of this, and while I've tried to 'push through', I haven't been able to do so in a productive manner. Is this common? How do I fix this?