Boredom.

You think boredom is sitting in a class you find tedious?
No mate, that's restlessness.
Boredom is that feeling you get when you surf the internet for hours on end, when what you're actually doing is trying to find a meaning to your life.

And frankly, I'd take restlessness over boredom any day because with restlessness, at least you know what you ought to be doing now instead.

The most unbearable part of this is that, applying this definition, I am almost certainly in a constant state of being bored.