I was musing on this myself earlier; the weekend before last was a major convention for me, and while I took nearly a week off of work for it, my brain hadn't really classified it as a vacation.

I think the major reason for it is not that I worked my arse off (as you do, when running conventions), but rather that essentially the entire weekend was spent in professional, get-shit-done mode. By the time Monday evening hit and we were at the Zombie Dog party (which would have been a perfect social cap), I was too sick to properly unwind, and just went home and went to bed.