After a couple of completely miserable days, I've improved to the point of semi-miserable. I came down with the respiratory crap everyone else has been having lately. Judging by other people's experience, I'll continue to have fatigue, headache, congestion and occasional coughing for several weeks before it clears completely, but at least I can do more than lay in bed like I've mostly done since Sunday morning.
Update, Tuesday afternoon: Spoke too soon. Several hours this morning with the worst chills and shakes I've ever had. Time to see the doctor.