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2.
Don't know where this one came from but it means to be tired and/or exhausted.

It propably was derived from "dragging your feet" but changed up to be a little more extreme and exclamatory.
I partied so much last night, that I was draggin' ass today at work.
by KJAM April 18, 2005
 
1.
1. Tired. 2. As if to be so tired that one's own ass is a burden to carry.
Ex. It's two o'clock, if I don't get some sleep I'm going to be draggin ass tomorrow at work.
by Last of the Kmart Shoppers July 10, 2006
 
3.
(adjective) 1. Tired, sleepy, unable to carry on.

etymology- Thought to have first been used during the Dark Ages. Upon surviving an attack from a fire breathing lizard, the last image you would witness before passing out from lack of blood and multiple contusions would be the "Dragon's ass", as it flew away into the night.
Man, I just got done fighting wizards and goblins and I am draggin ass.
by SwizzleStix July 24, 2012