One of the reasons people stay home is so they don't infect others. They might also need to burn a sick day for a doctor's appointment.
Agreed. I've also stayed home because injuries from a recent accident made moving painful, I had an allergic reaction that resulted in a full-body itchy rash and clothing hurt, and I recently passed out and didn't feel up to standing/walking/driving. None of these preclude sitting on the couch and watching TV, reading, or using my iPad. Even when I've been home with the flu or a bad cold, there is time between naps when I need non-taxing entertainment.
I'd say it's in poor form to post photos of you at the beach when you've called in sick, but other than that, I don't see any reason why you shouldn't be able to entertain yourself while you recuperate. In fact, I'd expect to see more
posts from somebody who is out sick than somebody who is at work.