In the past, I have come into work on my day off. I rarely do it as I prefer to have my days off. Have I gone to work at other jobs on my day off, absolutely. The other job that I had that I went to was greatly different from the primary job, therefore each job was, in effect, a break from the other.
In my humble opinion, I personally think that if you're going to take a second job, it should be so different from your "normal job," that you should be able to look at it as a weekend off from your primary job. You may end up working seven days a week, but, if that second job is restful, you can avoid burnout.
I did precisely that for about 2 1/2 years: I worked my primary job five days a week, and my secondary job was on my days off, and because both jobs were so different, I was completely able to not get burnt out. My wife on the other hand, was not so happy, because I was not home very often.
However, in the instance of being called in to work on your day off, make sure it's definitely worth your while. And don't do it often enough that your managers will think, "oh yeah, this person will come in without a problem, every time, so we called that person first." You want to be on the call list, but you don't want to think that you are "the go to person" for filling an open schedule slot.