(Why do we say that anyway? Are dogs usually sick? Do hotcakes sell especially well? Ah, never mind... )
Flu, most likely. Fever, headache, lots and lots of coughing, and a horrendous sore throat.
It's bloody miserable. My own fault. I neglected to get my flu shot this year.
Nothing to do but sweat it out. Excuse me, I'm off to bed again.