Originally Answered: What is art? How would you define art?
It's an excellent question, and of course is much more than painting, drawing, photography, etc. IMO, art is simply the expression of an idea or experience (see "Qualia") through creative analogies. Using this definition, many things could be considered art, so long as those things are being used as vessels to convey whatever "it" is you are trying to say.
Eating can be used as performance art (again, depending on what you are trying to say by displaying the action of eating). For example, perhaps your subject is your dislike of American consumerism. You could sit down in a crowded mall somewhere in America, fervently stuffing your face with hamburgers, hot dogs, steak, soda, beer, etc until you projectile vomit, and then continue eating until you vomit again, and then again, and so...causing a public scene. That would make a fairly dramatic statement about you feel regarding the subject, and is something that could easily be considered performance art in the artistic community (lol, not that I do, it just popped in my head)
The same could go with sleeping. In fact, much of my own art deals with lucid dreaming, and the play between consciousness and unconsciousness. In reality, you can use just about thing as an analogy, which means art can be just about anything...if executed in a "creative" way that gets a point across.
Another example, see Tom Friedman's "1000 hours of stare". It's a blank sheet of paper Tom stared at for 1000 hours. To someone without a fairly decent background in Art, or even Tom Friedman as an artist, this may seem ridiculous. But, when you delve into the conceptual complexities behind WHY Tom did this, you begin to recognize it as an ingeniously simple expression of who Tom is.