I think "calling in" is perfectly acceptable if you don't do it all the time. I work in retail and there is a boy who will call in EVERY time he has to recover the Grocery section. The worst part is when he calls in only an hour before his shift is scheduled to begin. This leaves the four people left in the store to start scrambling and trying to do everything they have to do and then pitch in on what this boy doesn't feel like doing. I, on the other hand, don't call out of work unless I need to for stress, my own health, or a family member. When it comes to work, I've called out a total of three times over three years. All for reasons other than "being lazy." Unlike most, I don't get paid for sick days. I only get paid for when I'm at my job, so I can't afford to call out. Which, if I could, I would probably be doing so tomorrow because my stress-level is insane and I deserve a laid-back day.
If you're going to call out of work, for whatever reason, try to do so hours before you actually have to come in. It eases the load for everyone because 1, someone else could come in or 2, the people who were suppose to come in later can come in earlier.
As for school, I skip it a lot. And this is college. I'm trying to do better and I will admit that this is where I use my "I'm sick" (read as: lazy) excuse. This is all a personal thing, where it will only effect you if you fuck it up (unless you skimp out on a group project). If you want to fail, skip as many days as you want.
So basically, if you need a day for whatever, take a day. Who cares if you're faking it. As long as you don't abuse the system, you shouldn't feel any guilt.