Work vs. Non-work

Today I went to work, but I really didn't work. I could not do this everyday.
How can you go to work and really do nothing at all and still be tired? I mean sitting around much used up some energy, but certainly not much.
How can people go to work everyday and do nothing and then not feel guilty when they get paid for it? I just don't feel like I did anything unless I actually worked. Not that work is really strenuous for me, but I still feel a sense of accomplishment after a full day. I feel like I helped in some small way. I feel like I made a difference, which is more than what some people can say after a days' work.