beaten and bruised

My job is not physical in any way.  I essentially SIT at a desk and use the computer.  I review files. I compile data. I analyse the information given to me.  I type documents.  I am sedentary.   The most exercise my job affords me is running to the photocopier/scanner or schlepping files to and from the file room or walking back and forth from meetings.  There is the commute every day.  The climbing up into the train, and the getting off at my station.  There's a long walk across the parking lot, and the occasional dash when I'm late.

Taking all of this into consideration... why do I feel so bruised and battered, and yes, even beaten, when I get home?  I am, quite often, left feeling completely stripped of everything good and lovely.  Tonight I am feeling that way.  Raw and wounded.  Frustrated and angry.  Tired and tearful.  I want nothing more than to lay down on the floor and sob.