When the alarm went off, I decided I was in no shape to even try to work, and went back to sleep. When I finally got up, and started medicating again, I figured out what I had done. This time took the correct dose. Actually, it all seems to have worked out, because I do feel somewhat better today, and despite the fact that I'm still coughing a little, it's not nearly as bad as I expected it to be. I think the overdose of guaifenesin actually helped a lot by ridding my lungs of so much junk so quickly.
In the meantime, we had a snowstorm, and there's about four inches on the ground. I so didn't feel much like shoveling this morning, but it was fairly light stuff, so I was able to just plow it out of the way with the shovel, as opposed to actual shoveling. I'm ready for spring.