Sometimes I am productive on days off, depends on why I am off.
I had my first sick day with my new company yesterday, I was just underslept and in a general state of blah, and I sat around and played vids all day. And in this case, it felt like the right thing to do. If I am off because I booked it off, I often end up getting stuff done that I don't have time to if I am working.
Sometimes a laze day is good, sometimes you feel too unproductive.