My feelings on this subject change w/ work load. When my projects heat up, 5 days don't seem like enough and 12 hrs is gone before you know it (because come Monday morning I'd rather not walk into a ***** storm that's been brewing over the weekend...). During periods of calm, I want nothing more than to slip out during lunch when no one is paying attention.
I agree with this. When I'm working on something complicated and/or interesting, I can easily spend 14 hours occupied with it, and complain there just aren't enough hours in the day to do everything I want to do afterwards. But put me on something repetitive and boring, and I'm ready to go three hours in.
And to the OP, doing a whole lot of nothing might seem like fun...until you're actually doing it. Vegging on the couch watching movies and playing videogames all day sounds like a blast, but after a couple of days, it somehow ends up becoming far more tiring and stressful than actual work.
I remember this one time, about 5-6 years ago, give or take, when I was stuck in the house for over a week due to a series of freak accidents causing my car to die from a cracked engine block. All my friends were busy with work, all my family and loved ones were out of town or heavily invested in other things. Since it wasn't a direct accident, my insurance wouldn't cover the cost of a rental, I just had to get a new car. The circumstances were perfect for me to just sit on my ass and invest in some entirely pointless, completely unproductive personal time.
And oh, I took advantage of it. That first day was great. I sat around and did nothing but watch movies and play videogames. It was WONDERFUL! Like being a kid again! The second day? It was alright. By the fifth day, I was completely lethargic, didn't feel rested when I woke up in the morning, and had a low level headache taking up permanent residence right behind my left eye. I was walking dead, exhausted in a way that was entirely different than the way you feel after a day of working. It wasn't pleasant.
Since then, I won't take extended amounts of time off doing nothing. Yeah, I'll take a day or two here and there. But if I have a week off, I'll have to occupy myself with something. Pure vegetating, as nice as it sounds when you're working, is a lot more trouble and pain than it's worth.