How to reduce the time spent on the PC?

Question

Health and computer

I sit at a PC at about 11 a.m. a day, not counting work. Sometimes I can not get enough sleep and because of this, either the back of the head hurts or my eyes hurt and get tired.
After working at the base, I play but also do one of my favorite things - photoshop. Various graphics.
Also, during my studies, I put off some important tasks, such as term papers, until the last.
It is addiction? Laziness?
Tell me how to stop sitting so much?