Getting sick?

I spent a good part of my evening wondering why I was so beat from my run. I just couldn't figure it out. Until it occured to me, I don't feel well. I never get sick. Knock on wood. But seriously, I really don't. I think the last time I was honestly sick was in 2002. (Fake sick does not count.) So when I don't feel quite up to par, I normally don't think that I'm getting sick. It's like a foreign concept almost. But yeah, I've got the body aches, headache and am incredibly tired. If I was going to get sick, couldn't it have been on a weekday? Jeez.