I'm sick and so might be the person on the other side of the screen
Having a fever, runny nose, coughing, getting nosebleeds every time I sneeze sick.
I mention this as a reminder that what you see of someone online isn't really them. It might be a close approximation of them (I do my best to keep them congruent), but it's not the same.
Maybe I can write a blog post or share a funny meme or the like when I'm sick. Or I could have a bunch of stuff already set up in the pipe using services like Buffer or DLVR.it.
And maybe I look like I'm online because I have chat clients that stay online, so it just looks like I'm "away" instead of "head pounding like a drum" or "asleep".
So remember that of the people you're interacting with online. You only get a facade, not the whole story.