Is the grass really greener?

So having been working full time over the summer, I have noticed one thing...it's so much more tiring than going to school. Now why is that? How come each night I come home from work I feel exhausted? I can't stay up as late as I usually do during the school year. Am I getting old? :O No way...I can't be!!! lol. But yes, hard to believe but I'm looking forward to going back to school. It's weird...when I was in school, I would look forward to going into the working world and now that I'm working, I'm looking forward to going back to school. I guess what they say is true, the grass does look greener on the other side...but is it really?