Thanksgiving trips...

I went to my parents house for Thanksgiving, unexpectedly. What is it about traveling that always makes you more tired than anything else? Sometimes I hate to travel because all you are doing is sitting in a car, and somehow it makes you tired. With all that rest, you'd think you would be all rested up, but when you get to where you are going, you're all tired. And the longer you travel, the more tired you are. What law of physics is this? Maybe I should write a reflection paper on this for my philosophy class.